It's not very complicated. The target is very large and slow, while the missile is very fast. I've done the math a few years ago, but with consumer-level optics

It's not very complicated. The target is very large and slow, while the missile is very fast. I've done the math a few years ago, but with consumer-level optics you could easily search a 40km diameter area for a 300m sized optics in seconds from a distance of 300km. Beyond that, you can use datalinks with a satellite (carriers are visible all the way from geostationary orbit), as well as two different types of targeting sensors on the missile, presumably optics+radar (which the Chinese seem to be doing), and obtain a very robust targeting solution. The TASM was retired because it's really just a worse Harpoon in everything except payload. It wasn't worth putting too much work into it. It's also 10x slower than a DF-26, and speed helps a lot with targeting. Also, the TASM was pretty easy to shoot down since it was big, slow, and not very maneuvrable.