They had different knobs available to them, and it's not clear given the opportunity that they wouldn't try it. E.g. it was less common for PCs to be connected to the internet and receive OS updates, so they wouldn't have an effective way of using a policy like that.
They certainly did their best to prevent any other OS from being on your hardware.
I think you can argue that current day MS is a little more afraid of anti-trust action than 1990s MS. Game developers were legitimately scared that MS was going to do this for windows and start taking their own 30% cuts from all PC games. I'm not sure if Valve confirmed it, but it seems likely that SteamOS/Steam machines were at least partly a backup plan for ensuring there was a place to sell games without MS skimming off the top.
They certainly did their best to prevent any other OS from being on your hardware.