Because then somebody applies for the top band, the company says they're slotted in the bottom band, and they've effectively recreated the situation as it stands before Colorado's worthless regulation, since they now have some 80k - 200k range which is effectively useless information.

Doesn't this happen already? In fact, that's how I got my current job, I applied for tech lead and they gave me an offer for senior and I took it.

The difference being I know the salary ranges of the bands before I apply and talk to HR

The idea is they have 3 ranges for 3 experience levels for 1 position, not a 80-200k range

It absolutely happens today, except today people in Colorado can also apply for remote jobs. It's an example of government trying to regulate and failing to solve the problem while only creating new ones.

If you list three levels, you end up with [i] a lot more applications to sift through especially at the extreme end of the spectrum (which might be an advantage sometimes, but often isn't) and [ii] otherwise perfectly hire-able people applying to the wrong bracket or anchoring their expectations to the top end of a bracket they're actually not at the top end of. Worse still, your existing employees see top ends of ranges too.

You also create the impression of massive growth (or team turnover) when actually you only want the one engineer.

You only list one position, with 3 different bands, but ofc we know nobody is gonna read that part.

It doesn't really matter. Particularly if you are looking for (actually) senior people with specific experience, unless you are very careful with postings you will end up with an avalanche of inappropriate submissions. Either someone has to wade through them, or you use a terrible filter that everyone hates.

You’d only list 3 levels if you’re actually intending to hire 3 different people, each at 1 of those levels.

They can. The companies not wanting to do it just don’t want to give more information to the sellers (labor), especially their current labor who might be being paid less while the buyer (employer) profits from the arbitrage.

I don't think it's that massive, especially because you should be figuring out a salary range within the first 1 or 2 conversations with the company regardless. For software engineers anyway, not sure about other less-hot markets.

Yes, this law will disproportionately benefit sellers of labor with a worse supply/demand situation. Price transparency is always better for the party (buyer or seller) in the worse supply/demand situation.

So maybe it should be limited to certain industries, like low skilled laborers and not white collar office jobs

Why? Prices are the signal to market participants for allocating resources. It is the whole basis of free markets and why they work.

What would society gain by obfuscated pricing? Assuming the goal is to benefit all of society, and not certain individuals who happen to be able to take advantage of arbitrage scenarios.