Apples and oranges.
Arsenal are a club that are sinking and badly need to turn things around. They're desperate to improve their defence, which is very shaky. They've got a young manager at the moment who's at a crossroads in his tenure, so they either back him to swim or let him sink.
We're very stable at the moment, winning, and have a glut of attacking options in and around the positions Grealish can play - namely a budding superstar named P. Foden. I really don't think he's going to 'move the needle' much, given the level of first string talent we already have. 100m in this market, for that position, is the type of money that should you get you a player who comes right in and grabs everything by the balls, automatic starter, changes the whole dynamic. I just don't see it. He'll be lucky to start the big games tbh.
In any case, the reaction of fans on here is completely predictable when the club gets called out for this of thing, so whatever.