Because while basic computation is a universal commodity, what is implemented on top of it certainly isn't - a piece of software always functions as someone's agent. When the systems you end up relying on are entirely defined by someone else, the only thing that represents your will is your mind, and it is effectively executing a complex and ill-defined protocol against always-diligent computers.
You've done the computational equivalent of declining a lawyer.
But it doesn't seem like a big deal, since you're only compromising a little at any given time. But the software is always changing in ways that benefit its controllers while your expectations are mostly based on the capabilities that they've presented. So the progress you perceive is entirely in their desired paradigm. Features that would benefit you but at the expense of Google/Apple/etc are never explored, because you aren't the user of their software - you're its working set!
I can forgive the old-timers who were conditioned by broadcast media to see the world in hierarchal take-it-or-leave terms and don't understand what they're losing by sharecropping in walled gardens. And I can mostly forgive the unclued herd that just buys whatever is advertised.
But for everybody who knows the power of personal computers yet pretends webapps and locked appliances are actual progress, either out of personal laziness, cognitive dissonance, or longstanding need for social acceptance: shame on you for abandoning that self-determination you tasted the first time you truly experienced computing.