I elaborated on that in a prior post. An Attack Option with a built in "negating option," like the reworded Polearm Master, is not an appropriate design paradigm for 5e. No existing O5E mechanics function with that paradigm, but similar concepts appear several times in new Level Up mechanics.
As a practical matter, it creates the "guessing game" scenario I noted, which is not "tactical" given that it's far too "meta" to describe as "tactics." To elaborate, an character judging that a foe with a spear will likely take a poke at them as they close to melee, but they need to take them down to aid their allies, resembles a "tactical decision." Deciding if they will close to that foe and avoid the attack, or save their reaction for the possibility of a Press The Attack against them, or if they will Fall Back from a Fighter's Press The Attack and risk a Rogue's Press The Attack, is well beyond "tactical" consideration and adding to the "meta tactics" and "guessing games" that detract from a game, rather than adding to it. Add on the fact that the detriment of Fall Back, outside of using a Reaction, is Disadvantage on attack rolls for the character using Fall Back, and how this does not impact many spell-focused characters, it is a flawed mechanic. It could add that, in addition to Disadvantage on Attack Rolls, characters who cast spells following Fall Back have their spells resisted with Advantage, to make it less of a "no brainer" for casters, but at this point it's already clear the simpler answer is to scrap both Press The Attack and Fall Back.
PTA and FB add too much complexity, imbalance, and meta-game guessing games relative to what it offers at the table, in short.