You know what, I'll give it ago. Seems like a fun topic to discuss. I don't think the issues is the wrestlers are shit though. What I do think the reasons are
1-Different writers-Imagine if a novel series suddenly changed authors midway, would you think it would get better or worse? Obviously it would get worse as the new author did not create the story or character and would struggle to recreate what was so great about the original stories. In the same way, a huge amount of talent have suffered from the transition from NXT writers, to main roster writers. The main roster writers would struggle to get what got the wrestlers over in the first place and are generally not in tune with the capabilites, strengths and weaknesses of each character. This is made worse by Vince who forcibly molds these NXT characters to his vision despite not really getting whats so great about them.
I was gonna list examples but I realized every wrestler from NXT has almost over simplified or changed their characters to something worse. And I mean everyone. Nakamura has started to show signs of it. Vince thinks audiences are just attracted to his weirdness which is why the commentators are caling him the artist known as Nakamura. Owens started of with his NXT prizefighter character, but eventually chaned into a chickenshit heel that Vince thinks all heels not named Brock Lesnar must be. American Alpha are charismatic and great wrestlers, but they are nothing aside from being 2 great amateur wrestlers in terms of character. Vince sees Balor as the Demon and only the Demon which is why we lnow nothing about normal Finn. Vince wanted Zayn as an underdog, so he makes him lose every feud and title match. The reason why Zayn hasn't flopped hard is that he was actually given character development which brings me to....
2-Character development-Character development is important in every storytelling medium. When a character develops and gains layers to his personality, it becomes much easier to relate and get emotionally invested. The problem with NXT is that almost every characted has developed and reached his full potential while in NXT. So when he comes to the main roster, theres not much left to develop. This leaves the main roster crowd starving for a reason to get emotionally invested in the wrestler.
American Alpha are amazing in ring and charismatic but nothing about their character has been developed from 2 amateur wrestling dudes. Balor has no
character development. Crews, and Kalisto has not changed since coming on to the main roster. Bayley'd character has actually undeveloped. Bayley's character evolved from this wide eyed fan to the veteran that everyone respected and wanted to beat. It was that journey to the top and how she chamged that made people love her. So she goes to the main roster, and her character reverts back 2 years despite her achievements and it just does not work. Bayley isn't this rookie anymore. She's a top dog so it becomes harder to buy her as an underdog.
In comparison, Shibata's feud with Nagata. It was about Shibata learning to respect a veteran and be more modest. In short, Shibata's characted developed and it caused fans to emotionally invest. Almost all feuds in WWE have no development now and when casuals don't get invested people blame it on the wrestler not being entertaining or charismatic enough when in reality, no character development equals no reason to care. Its only the hardcore fans who know of the wrestler's beginning and are already invested in him are the ones who stay. The more that I think about it, this might actually be the reason why casuals are leaving. There is no character devlopment for them to care, therefore stay.
3-NXT's lack of emphasis on promo skills. Make no mistake, NXT is a development brand. Its just the NXT that we watch is the ones who are ready to be on TV. Despite this, NXT has always suffered in promos. No sugarcoating it, too many guys there can't cut a promo and they still haven't improved that aspect. I don't know how, but get acting teachers or public speakers or something and train them to speak better. Its just not as noticeable on NXT because theres not a lot of promos and the ones that are given time are already good at it anyway. How
4-Getting called up before ready-How did anyone think calling up Nia Jax, Dana Brooke, Apollo Crews, Carmella and Mojo Rawley were a good idea. Its just pure stupidity. You don't call up the guys who are still honing their skills and still haven't won the main title. They still have stuff to do, and things to learn and its gonna continue to happen. The worst part is when they are brought up without a plan. Crews and Breeze were brought up for no reason aside from to die on the main roster. There was no plan for him, none whatsoever. I don't wanna claim sabotage, but its obvious that some guys were definitely sabotaged. The ascension were obviously screwed on the main roster it wasn't even funny. There a decent team that if given a push can be taken as a threat. I still remember that Smackdown tag team championship math where they came out last and the announcers sold it so hard that Alpha were fucked and the ascension could win that I almost believed it. If only they had that booking at the start.
Its a long read, but heh I'm proud of it. Now I just wasted 30 minutes writing this instead of studying