Simply put it would create too many problems. At his peak the Sentry could solve most problems by himself.
Take Thanos for instance: If he was at the first showdown couldn't he have simply speed blitz Thanos and taken him out? Why would Warlock or Mar-vell be needed?
The same goes with being on a super-team. The only reason he works now is Bendis is using his mental problems as an excuse for him not to operate at full power. If the Sentry did not have these mental problems before he was forgotten than teams would be unnecssary.
Also, it raises the question. Even if Strange was able to erase the minds of everyone on Earth why was he able to erase it from the memories of characters such as Galactus? Can Strange rewrite reality now?