#TLDR: Ocean lost hashrateA couple of weeks ago, Ocean pool's hashrate was on the rise, and they briefly touched 20 exahash -- almost 2% of the total. But since then, they've been on a decline, even getting as low as 10 exahash this week.
Why are miners dumping Ocean? I can't say for sure, but if I had to guess, I would guess it is because some of Ocean's major personnel (Luke Dashjr, Bitcoin Mechanic) are seen as champions of a controversial UASF called BIP-RDTS. (Weirdly, I am also seen as a champion of this proposal, even though I have publicly stated my opposition to it several times.) Miners may be worried that Ocean will start enforcing this soft fork and they could end up on a bitcoin fork with a minority of hashrate.But it's sad because Ocean is the only pool on bitcoin that currently lets miners mine their own block templates, other than some "solo pool" options.There are two other pools -- Braiins and Demand Pool -- which have said they will offer this feature at some point, but they do not seem to currently do so.As a result, if you are a miner and want to mine your own block templates, Ocean is currently the only way to do it in a semi-normal pooled setting. But there may be a UASF stigma associated with them now, and many miners seem to be abandoning them. Hopefully Braiins Pool starts offering miner-controlled templates soon.