MEV and censorship questions?

I came across the MEV watch website (https://www.mevwatch.info/) and wanted to learn more about how exactly transactions are getting censored. I have done a lot of reading but still find myself scratching my head around the intricacies of censorship as it pertains MEV.

My understanding is that ever since the merge, when Ethereum went from Proof of Work to Proof of Stake, the process in which blocks are built have created a vector for censorship. MEV or Maxium Extractible Value is a sort of strategy where the block builders (miners or validators) can rearrange, include, or exclude transactions to maximize their profits. "MEV Boost" acts as a mediator that can be used to give the validators a fair share of the MEV extracted.

The problem is that MEV Boost is also complying with OFAC sanctions and has a blacklist of ethereum addresses that have been sanctioned by OFAC. Validators who run MEV Boost are effectively excluding any OFAC sanctioned Ethereum addresses from being added to a new block, which is censoring those addresses from interacting with the ethereum protocol.

My questions are:

1. Is my understanding above correct?
2. Why did this become an issue post merge, how come Proof of Work did not have the same issues of censorship?
3. Are those OFAC sanctioned Ethereum addresses completely blocked from transacting or are they just being ignored by the validators that are running MEV boost but they can still get included in Blocks from validators that are not complying with OFAC sanctions?
4. On the mevwatch.info website it has a "censorship offenders leaderboard" which lists the validators that are censoring transactions. I noticed the biggest offenders are the largest validators like LIDO, Coinbase, Binance. I am assuming they are required to block these transactions, however it appears that only some of their validators are censoring transactions. For example: for Coinbase it shows that they have roughly 800 validators, however only 472 are censored which is 58% of their validators. Whats the deal with this? How come they are running some censored and some uncensored validators?

Any insight or even a better explanation would greatly be appreciated.