The reason they did it was loss of buyer confidence - apparently they interviewed a bunch of buyers who had left eBay after bad experiences and they came to the conclusion that there was an unacceptable level of feedback abuse being perpetrated by sellers (this is probably true - there certainly do seem to be a lot of sellers who have been bullying their buyers into either withdrawing negs, or not leaving them at all, when in fact the sellers truly deserve them, or just leaving retaliatory negs). Ebay took the decision as a business to make a bold move to try to win the trust of buyers by offering them blanket protection against this.
I’ve suggested this myself - it would need to be a bit more complex than that to avoid causing brand new problems, but apparently this option was considered and rejected, as it is already in place at some other site in which eBay owns a non-controlling stake - and apparently it doesn’t work there in a way that they consider suitable for eBay
Personally, I think the new regime is morally repugnant, as it stands - being told that you can leave feedback, but only if you say something nice, is just wrong - skirting the Orwellian. They shouldn’t call it feedback - If it must be changed so as to prevent some people saying nasty things, then perhaps they should just scrap feedback and replace it with hard facts - number of transactions completed, number of strikes, number of disputes lodged (broken down to open, upheld and denied), number of disputes received (broken down similarly).
But I also think it will cause problems. Seller feedback ratings will inevitably settle toward a lower average - and this could affect newbie buyer confidence just as badly as the problem that is supposedly being solved.
Also, there is already a low-ish level of buyer fraud - I would expect the activity of this contingent to grow - immune to negs, they can make all sorts of unreasonable demands of their sellers (free postage, or I neg you; partial refund, or I neg you; I’ve broken this and I want a refund, or I neg you, etc).
eBay says than in the absence of seller’s ability to neg, they will seriously investigate any reports of bad activity and deal with such abusive buyers - but based on their track record with that sort of thing, I have absolutely no confidence that they will actually do it.
So yes, it will probably nail one category of crooks on eBay - the big, bad sellers, but I think it will cultivate a different category of crooks to replace them.