Obsidian Entertainment was rumored to have a market cap of roughly $10,000,000 - which is really not a lot (and why they kickstarted so much).
Electronic Arts has a market cap of roughly $30,000,000,000 - meaning that if you would need 3,000 Obsidian Studios to make up a single Electronic Arts. Even if the numbers aren't exact (they're rarely disclosed) - Electronic Arts is massive compared to nearly any other studio. There's a 0% chance that Microsoft purchases them until Phil Spencer is able to turn around the ActivionBlizzardKing acquisition.
There's also the issue that EA doesn't have a lot of valuable IPs left. A lot of their popular titles are licenses (NFL, CFL, NHL, F1, (formerly) FIFA, PGA, WRC) and not IPs, Microsoft could just try and work out individual deals instead. If you take out Sports Games - you have a Star Wars Licensed Game (Jedi - Fallen Order), Dragon Age (dead, LOL), Mass Effect (dead, LOL), Command and Conquer (dead, LOL), and so on.
I can't see any real reason to buy EA for Microsoft (or anyone).