Well, for one, if Google's ML decides to nuke your account, you lose your photos unless you have a blog, a lot of upvotes, and luck.

This is gonna be a risk with most cloud services. No matter what, you want to have a backup anyway.

Because they are known for bait and switch; and even worse bait and shutdown? One bad click, or their AI screwing up might lock you out of all your photos and entire Google a/c? Among numerous other reasons.

So while at it move away from one more Google service.

Is the bait an switch comment fair? Google have offered free photos for years and obviously the storage requirements must be growing huge. A business needs to be able to change.

Also haven't they said on both the big changes anything in the past will be held as legacy under free and future uploads will go to storage? I think you have to accept business needs to adapt models sometimes and Google Photos is more this than bait and switch.

Fair call on the lockout. This is a real issue for Google.

They starved out any other provider who could offer photo storage with their free storage. Now they discover they need to charge for it.

Is there any convenient way to back up Google Photos to Backblaze or S3?

There are afew projects on github that let you configure an API key for google access and pull your photos, without using takeout. https://github.com/dtylman/gitmoo-goog https://github.com/gilesknap/gphotos-sync

I run one on my wife's account with a cron job to grab new photos daily.

Sure, just get a google takeout of your photos data, and whatever else you want backed up, and stick it in S3.

They've clearly indicated a desire to try another platform. Why does it matter what the motivation is?

OP mentioned that google is ending the free version, it makes sense to ask them why they don’t pay.

If the reason is because they want a free tier forever, that impacts the recommendation. If the reason is because they think google could shut you out, that may need a completely different recommendation.