That's probably because people know that rx580 graphic cards will be the cheapest of them all once merge on Eth is activated, that gpu is getting older every day but still capable, now that we have awesome AMD gpu like 6600XT I wonder why people will leave this for RX580s.
Correct. Efficiency will become the king again. GreedForce RTX 3000 cards, especially the LHR ones, will hold their value the best. Not a bad deal considering the LHR cards are still a bit cheaper for the same profit, as long as you run dual mining.
I think that after ETH PoS, these will be the numbers for an RTX 3080:
Cost of an RTX 3080 (after tax) w/system parts + cooling + utilities: $350
Revenue for an RTX 3080: $0.90/day yearly average (range: $0.70-$1.10/day)
Power cost after tax @ 7¢/kWh: $0.27
Depreciation @ 30%/year: $0.35
Net income: $0.28/day for 360 days = 33%/year return
If you sell as little coins as possible (to cover rent/power) and HODL the rest, you could make a 300-800% ROI if another GPU gold rush happens in a year or two. You could then sell most of the video cards too.
At least these were how the numbers worked out during the 2019-2020 bear market.