I've written a lengthy reply to a question under quochuy's weekly witness report. I'll quote some parts of it and try to elaborate.

... This does not mean someone in the Top 20 witness is swimming in money in most cases (arguably). They might be spending thousands of USD every month just to provide services for Hive users. (@blocktrades, for example, api.hive.blog is a cluster of hived and hivemind nodes, that is not cheap to do. Not to mention actual core development work without any DHF proposal whatsoever.) This does not necessarily mean that blocktrades is a philanthropist. He just believes in the ecosystem and wants to contribute, paying out of his own pocket if need be or barely breaking even with witness income. If Hive was $5-10 USD, his and his team's work would pay off greatly.

Personally, I have been a witness for more than a year at this point, majority of the time I was a witness, Hive was averaging at about $0.12 per Hive. I was ranked ~60-80 during the year 2020. So when you consider my income, I was not breaking even at all and was paying out of pocket each month. I currently run several different services on Hive (one of them being api.deathwing.me, one of the most used nodes.) that require beefy servers that cost a lot of money per month to run. Thankfully, as of writing this post, I am witness rank 34 on the blockchain. If you look at my account history, you can observe that I haven't powered down once just until a month ago, and still, I only power down enough to cover costs for running my on-chain services.

Quite a few of the witnesses in the top 20 are "project accounts" (i.e. @steempress, @ocd-witness, @peakd etc.) as well. (Who powerdown and powerup their main accounts).

That aside, it's hard to pinpoint the expenses of witnesses. Some might be spending more than others while some spend less. Some might have projects that require constant upgrades/additional servers and/or funding to pay for services/employees etc. Or simply, they are simply paying "themselves" for their work. An example, developers. The current powering down spree might be due to a similar thing. When Hive's price was quite low, it is possible that some people had to forego any profits if not paying out of pocket.

I've said it before, I'll say it again. I do encourage everyone to run a witness node. Not for profits, but for the chain's stability. As well as encouraging anyone who have the ability to do so, to run a full node. Currently, there are only 8 stable full nodes. (Beacon) The more would always be best. Different locations, different countries, different machines, different operators. Always good for decentralization. Not to mention lowering load per node, potentially making everything faster as opposed to thousands of people (lets not forget bots) using the same node.

The crypto world has a beautiful acronym. DYOR. Do Your Own Research. It would be quite good if rather than proxying to various accounts and leaving it be, everyone actually invested some time and researched witnesses and see what they're doing to contribute to the chain and alter their votes accordingly.