Amazon is definitely the wrong place to look for products in this category.

Do you know what the right place is?

I don't work in this field (just adjacent to it), but I would start looking at Digi-Key, RS, Mouser, Farnell. It might be that people working in power electronics have other go-to suppliers but I'm not familiar with them.

Current for charge controllers scales really nicely with horizontal scaling, there isn't a huge reason to do it. With that said there can be various reasons to want higher VOC in a single string. Managing voltage drop, and value engineering on conductor size. The marketing on those is often aimed specifically at max input voltage, rather than charge current because of this. Victron is probably the prime example of higher end stand alone MPPT controllers.

These days, I recommend using DC optimizers that are attached to each module. They provide MPPT tracking on a module level, and make engineering calculations simpler.

They are also much cheaper than microinverters, safer, and more reliable.

Any specific examples that you would recommend?

Tigo optimizers are nice, and you can have just one optimizer for 2 modules. It's mostly meant for commercial bifacial modules, but it can work just fine for 2 completely separate modules. You can also use their cloud monitoring thingie to remotely track each DC optimizer's health.

Or you can use SolarEdge optimizers, they are simple and cheap (<$100 per module).

Both support automatic shutdown, so you can safely de-energize the entire system if needed. It's a problem for classic string inverters.

Most of the inverters for this are mostly installed by solar companies and so you tend to find them more on specialist websites dedicated to solar gear. Its the same with solar panels there is a very limited set available in standard retail channels especially of the 400W size and output.

See the recommendations on /r/SolarDIY or just look at EG4 or Victron as a starting point. The prices for EG4 are very decent.

Probably because you can't generally install them yourself, and you need a licensed electrician to do that.

A licensed electrician is not required for this in most places in the United States.

That's incorrect. California and Arizona require a licensed electrician to hook up inverters to the grid. I have not checked other states, but I'd be surprised if it's not the same.

And most of the more powerful inverters require a grid connection because they can't work in an "islanded" mode.

Are California and Arizona "most places?" Most states allow homeowner electrical work.

Victron makes plenty and are very high quality