The big thing that happened to power tools was Lithium-Ion batteries. All of these companies competed when they were still corded electric tools. You could just make a really good drill or saw or router.

Interchangeable batteries got really good and made every set of tools a platform. More importantly, there are only a handful of sources to get batteries from. For all these companies to differentiate and compete they needed to insert their products into wide lines of platforms.

The larger factor here is batteries are expensive enough that you don't want to mix and match. There is no reason your corded drill and saw need to be the same brand so you can choose whatever. However if your cordless drill and saw take the battery that means you don't have to buy as many batteries (or alternatively when your drill battery goes to the charger you take the saw battery instead of being unable to drill any holes).

Though people are starting to figure out that there are only a couple different batteries and so a cheap adapter means you don't need to buy all the same anymore.

Yeah if you look at the power tool industry as a whole, over the last 20 years has seen massive improvements in quality across the board.

Cordless tools were a niche product, they could barely run an hour and they didn't have 1/10th the power a corded tool does. Things like cordless angle grinders didn't even exist because there was no way to get the required power to drive them.

You also have the advent of brushless tools recently which drive even more power to cordless tools. Smaller, lighter, more power and longer runtime. You put a cheap 18v Ryobi driver against an all metal housing Craftsman corded from the 80s, that cheap plastic Ryobi will outclass that Craftsman every time.

Some brands have risen and fallen. What's happened to Porter Cable is a shame. But conversely, how completely competitive a brand like Ryobi has gotten is also a near miracle. It's a great time for power tools!

This is why I evaluate if a tool type needs to be cordless when buying. Drills, impact drivers? You want cordless, or to have the option. For a circular saw being used by a homeowner for most DIY purposes, it's worth any arrangement issues to have corded. The cordless ones tend to take less common blade sizes and eat batteries even with the provided extra-lightweight blades.