I have seen so many 20 twinks recently. What changed?
BFA's last major patch, blizzard separated XP on and XP off. a move like they did back in WOTLK. twinks and levelers were merged in Legion due to BGs using templates, enchants being inactive, etc.
when BFA started BGs were still merged but no longer fixed template. so all twink brackets became more active because they could get BG pops, gear, profs, and enchants made a difference again.
after the separation 2 months ago, many brackets died. many players who focused on twinks and various brackets could no longer get BG pops along or lack of interest in BFA unsubbed. they either made vet20's before they unsubbed, or added a trial to their main Bnet account to play. some who did this also say they plan on doing Classic WOW where blizz allows twinks to pillage ill geared players who venture into low level BGs.
another changes was to the 20-29 bracket, blizzard moved F2P-20 and vet20's into XP ON. this left twink 29s with no BG pops, so now some exploit now. BG pops on NA servers with include OC, SA servers too is 6-9 minutes, 13-15 minutes on way off late hours.