Lesnar could always get screwed out of the title at fast lane against someone and he'd get his rematch in a triple threat at WM. That's if Lesnar actually shows up at fast lane and we don't get a tag match as the damn main event.
WWE might be forced to put Bryan in the main event again.
The Reigns vs. Lesnar feud hasn't even started yet. At least wait before you pass judgment.
Also, last year Bryan got in the title match because the Authority prevented him from competing in the Royal Rumble. It was, in some ways, an act of fairness or retribution from the Authority to Bryan.
This year, however, Bryan lost fairly to Bray Wyatt, a wrestler with no ties to the Authoirty. Bryan, thus, has no legitimate claim to be in the title match. Roman Reigns won the Royal Rumble, so he deserves his moment.