ELI5 Exactly Why Validator Client Diversity is Critical to The Merge

Superphiz just posted another video stating how the ethereum network is in an emergency if it doesn't resolve client diversity in the next two months.

https://www.youtube.com/watch?v=RQcP1y4yGms

To me, his video comes off as bullying and gaslighting prysm users and the prysm team. Using an analogy that prysm users are alike to alcoholics that do not care about anyone but themselves. Which I think only accomplishes painting prysm users as bad guys and dividing the community, which isn't helpful. I'm not criticism superphiz for phrasing it that way, and I highly doubt he is trying to intentionally paint prysm users as bad, it's just how I take the analogy he used.

Every reason I hear is "Prysm has a supermajority, this is unhealthy for the network, there are a ton of known bugs when a client has a supermajority that will likely prevent the merge. prysm should take ownership of this issue"

I believe having specific details is more convincing than blindly trusting someone's word that something is unhealthy. It takes time, but people really do listen to convincing arguments based on reason and evidence. So that's why I'm asking for an expansion and specifics in what's being said, it will help both sides.

Additional question... if client diversity is critical to eth2, why wasn't it built into the clients and protocol? We already know people are less reliable than computers, so I feel if client diversity was important the devs would've coded it in. Therefore, it's either not important or the PoS devs had a horrible oversight in not including client diversity at the protocol level.

And would it not make more sense for superphiz to write an EIP to have client diversity built into the protocol layer? I know I've seen some discussion of deducting eth from those accounts who run majority clients. If approved, that seems like it would be the end-all to this topic.