A RWC final is a hell of a lot of credit in the bank; as are some of our performances that year. Eddie has proven that he get performances such as Away to Ireland, or RWC SF again NZ. He is proven to have the capacity to do that. That counts. A lot.
2018 was poor, and visibly so for exactly the reasons Eddie told us it would be beforehand.
2021 is poor, a significant proportion of that is for exactly the reasons Eddie told us it would be beforehand (though that doesn't explain our indiscipline).
A poor run of results needs to be an actual poor run of results. Yes, we want good performance, and put more weight on that than results - but most fans don't, nor do the RFU.
Any coach deserves the chance to turn around a poor run of performances - and if it's for reasons he's explicitly told us about beforehand, then the time-frame is already set. It's not like Eddie has no idea why we're playing poorly - he explicitly told us the reason (he's got a new attack system lined up, but isn't going to put it into practice yet - partly to not show his hand, and partly because we're seeing new ref. directives, and the plan will need adjusting to that before being applied).
Robinson in contrast, had no real credit in the bank, and didn't know why we were playing badly, or what he could do about it.
We've been playing below par since January 2020 - with significant disruption from Covid; and in a way that was predicted (literally every losing RWC finalist has had a bad following year); results have started going against us for the last... 3 matches - well, 2 out of 3. Eddie has absolutely earned the right to make amends - and that doesn't mean making significant changes mid-tournament, upsetting plans, and almost certainly backfiring. For me, he gets the Summer and the Autumn do show what he said he would (an attacking plan that isn't just to hoof it and defend further up field). If there's no sign of improvement by Christmas 2021, I'll start questioning, a bad 6N '22 and I'll call for his head.
In terms of time - 2 years isn't enough time for a new coach to put new processes, and new game-plan in place, tinkered to the real world and polished in time for a RWC. We're too late to do that unless promoting from within and continuing Eddie's grand plan without Eddie.
1 year is longer than you can expect a dead-cat bounce to last if it's change for change's sake. We're too early to make the most of a bounce for just providing a change.
RFU were struggling for money before Covid stopped them allowing crowds in for rugby or concerts.
ETA: What BPM said