The training system is now FUBAR.
Was a time when a young (18-21) player, using my usual daily training system, would gain 20% a season. My young players last season gained between 10% and 12%.
I used GK training to get my 4* youth graduates and 3*-4* 18yo Transfer Market purchases up to 101% to make them usable, and to match the rest of the squad. This is now denied me and other 'normal' methods of training don't give anything like the improvement for the same number of green packs.
So my teams are gradually dying while other teams I'm matched with are either inveterate Tankers, or filled with friendly-boosted mutants or token-rich scout-bought 6*-7* players.
So when you say people won't quit/aren't quitting over the removal of GK-training I don't believe it, because this manager isn't going to last long without some way of effectively training his squad. Whether that appears with TE2019 remains to be seen.