Sure you can. For instance, I don't use Exchange at all.
Whether or not viable alternatives exist, those alternatives don’t magically change org structure, office politics, budget, current business priorities, etc.
Bottom line: many people managing exchange don’t have the luxury of evaluating this problem in terms of alternatives.
People used a few different groupware solutions, worked with bespoke IMAP installations on Linux servers, or (the vast majority) had on-premises Exchange servers running locally. It all required lots of tech wizardry, tinkering, duct tape and hope.
It was a long while before we had turn-key solutions, and you needed actually knowledgeable folks running your IT operations, and nothing was as fully integrated or cheaply available as Exchange Online.
a.k.a. i think you're missing the point. It's ok. You want knowledgeable people running your key infra. Outsourcing that to a company that doesn't respect privacy seems to be shooting oneself in the foot.
IIRC as they've been acquihired they had their own software stack back in 90's.
Getting email right requires lots of infra expertise, steady financial expenses, and time. Most companies just don’t have any of these available, and it makes zero economic sense as well if a product like Microsoft 365 exists.