Now that Barry has to start carefully calculating every one of his moves to try and prevent Iris’ death in the not-too-distant future, Wally as Kid Flash might be too big of a variable for Barry to want to trust on his own.
The stakes are almost impossibly high with Iris’ life on the line, and there’s just not room for error now that Barry has resolved not to mess with the past anymore.
He even endangered his life on the off-chance that he could spark superpowers in himself, and he hasn’t gotten any less reckless since becoming a speedster.
His enthusiasm to want to help people is endearing, but his tendencies to ignore orders and follow random impulses have put people in danger.