Because corps need stuff that's mass produced and stable. An amazing gun that takes months to learn how to fire it in particular is pointless, as the guy who they are giving it to is probably going to out before they learn how to use it. A program that needs a programmer to constantly modify it so it doesn't crash is a liability, no matter how well it theoretically works. It also isn't like B2B sales don't include the same planned obsolescence that consumers get hit with.Except if you're going to use any of this stuff to fight against the corps, and the corps are also fighting against each other... Well, then that means the corps are trying to build exactly the same things you want to use, and they have more time, money, and technical know-how to devote to the project. And in actuality, why would a corp develop all its tech in-house if it doesn't need to? Really, they're just going to buy all their security and espionage tech from other vendors, who, again, have dedicated far more resources to the problem than you can ever hope to on some back alley street. They may not be goods for the general public, but they're still made and sold by companies for a profit--stuff you can order from a catalog.
They keep up, especially for the most important things, by throwing money at the problem. Is their stuff the best? Hahaha... no. But it does the job and holding out for better would probably waste more money than its worth. The world will have "gone right for capitalism" because you can get huge amounts of very consistent stuff cheaply and easily and that's exactly the sorts of things corporations need to function well. It just isn't what PCs want. For PCs to get what they need they need to find the exceptions.
I'd have the tier list be Mass produced stuff selected by someone with a budget and/or knows what its for<Stuff selected by someone who knows the market like the back of their hand<Stuff custom made by an expert for their own use and people who can go "money is no object" when buying it.
Most antagonists are going to be in category 1, but important locations and people are going to be 2s and 3s. PCs are mostly going to be 2s, with those built around a particular piece of equipment going to be 3s. Normal people aren't even going to get to 1, as they don't have the resources nor the time to do that well for most of their stuff.