Every country and every army has limitations, also nothing can be solved by only military power. There are many geopolitical aspects of every move and Turkey needs to balance every side to protect itself. Trade relations, security, economy etc. everything should be considered. If you eradicate YPG completely and kick USA out of Syria, what will happen? Complete Russian control over Syria and we don't know how Russia will act.. More refuges for Turkey? Do you think Turkey could keep idlip, afrin or jarablus under control if USA leaves? This is a long chess game.
Now Bidenopoulos is ruling USA. even if Turkey wants, relations would not be perfect and Turkey and US cannot get too close. Russia knows this so pressures Turkey in Syria to increase gains in the chess game. Turkey and Russia are carefully playing this geopolitical chess since 2015. This is an hate & love relationship, both countries are tied and depended. YPG could even get tanks & jets but they would never become a player and never survive. When US is gone ypg/sdf will be eradicated.
Unfortunately government of Turkey invited all these players to her border. They should have seen this outcome before weakening Assad and Syria. But on the other hand despite good relations in late 2000s, syrian regime deserved this long before. That is what happens when you turn all your neighbours to enemies.