Microsoft threw billions at it and became the third player. Sony also threw tons of money at it and succeeded. You don't need revolutionary ideas as a hardware publisher, you need the willingness to lose money for a long time to get a foothold.
Willingness to lose money is necessary but not sufficient. You still need to do something that nintendon't. Sony was lucky in that Sega completely bungled their entries into the 32-bit era, and Nintendo chose a cartridge-based system at a time when cartridges were on the way out, so in reality, the Playstation was the only competently-executed CD-based console available at the time.
Similarly, the XBOX was kind-of revolutionary. If anything, it was ahead of its time. It had a built-in HDD, its controllers were logically USB even if they had a proprietary form-factor, and it had built-in networking, and it didn't use any fancy nonstandard architecture. These are all features that would eventually become standard, so MS definitely had good ideas, and by doing them first they were well-positioned to do them right again. If MS had brought literal nothing to the table, I doubt the 360 would have been able to capitalise on the PS3's various shortcomings.
EDIT: "Doing something nintendon't" might be more literal than I thought. If the real market for Stadia is casuals, then what does the Stadia do that the Switch doesn't? I guess from reading the Reddit thread linked elsewhere, that the main market was ex-PC-gaming dads whose wives wouldn't let them get a new gaming PC. Which makes sense, as those people aren't interested in playing Mario or Zelda. But that's not a big niche to be targeting.
