There's no reasonable finish to this match without interference. Suspension of disbelief is severely strained when you've got a monster of a man up against this aging vet who looks worse backstage every consecutive year.
not surprised Vince made that decision (and Brock just did 1 clothesline & 1 F5 anyways so not like they had him go all out)- There are people within WWE who believe that Brock Lesnar should have been booked differently and as more of a threat to The Undertaker, since the only point Lesnar did anything to Taker was the go-home angle on RAW this week, and that was still a sneak up from behind distraction with the announcers calling Lesnar a coward.
The original feud between Taker and Lesnar that was talked about in 2010 had Taker proposing that Lesnar beat him to end The Streak, although that was never seriously considered, thinking it would be the right thing for business. Feelings on The Streak have obviously changed since then.
Vince McMahon made the decision that in the build for this match, Taker never gets touched. He was smart enough to change that rule for the final build this week on RAW.
Source: Wrestling Observer Newsletter