That does happen, but I think it's only done with fixed platform structures[0], rather than the mobile platforms like in the article. Apparently 532 rigs have been turned into reefs in the Gulf of Mexico[1].

[0] https://en.wikipedia.org/wiki/Fixed_platform [1] https://www.bsee.gov/what-we-do/environmental-focuses/rigs-t...

Surely they're absolutely filthy and you don't want all the paints, oils, lubricants going into the water?

Some can and are decontaminated and sunk for creating reefs. I dont think old oil tankers are used for obvious reasons.

The reason why I thought about this was because whenever you look at any world war timeline shipwrecks, it is totally overtaken by aquatic life. I am sure those ships had enough toxic things on them maybe radio active stuff too but somehow nature reclaimed it.

Too much value in the steel and other materials, I'd guess. Sounds like hard and dangerous work for people cutting them up, but it is work, probably in areas without a lot of other prospects.

The rig was worth about $3 million as scrap in Turkey, according to the article ($190/ton at 17,000 tons). Approximately $0, maybe less, if the owners were forced to send it to an EU scrapyard, as regulators keep threatening to enforce.

At that price level, sinking it to create an artificial reef for environmental or tourism benefits is a competitive option. Though there may be other reasons it's not best suited for that.

It's happened with production platforms. I assume in the case of the exploration rigs, there's a positive ROI to towing them to a ship breaker and selling them for scrap.