We compel businesses to all kinds of speech, for instance, they have to specify what kinds of ingredients their products contain, and their nutritional value.

Regular everyday people are allowed to lie in their private lives if they wish, but try lying in an advertisement and see how it goes. There are strict rules on what you may or may not say as a business.

There's a huge difference between compelling not lying vs compelling disclosure. We do require disclosure in some cases like in the ingredient example you mention, but even the it's limited to what's necessary: companies don't have to disclose exact recipes and can hide a lot behind the "flavorings" label for example. I'm not sure if forcing disclosure in this case is good, but I do like keeping a high bar on that in general.

Businesses are not literally people. Treating a business as a legal person is sometimes convenient, but there is no reason to cling to this fiction in all circumstances.

Even if they are, is salary range disclosure "compelled speech?" Businesses, including sole traders, must disclose their revenue to tax men. They might need to disclose contact details, address, packing dates, product origin...

Businesses cannot speak or write though, only people can.

For the same reason we require businesses to serve anyone, regardless of race, color, religion, or national origin.

The social benefits outweigh the harms.

Just about any law can be boiled down to “compelled speech” or a restraint on speech if you twist it enough. Actions are speech. Murder is an action. Criminalizing murder is criminalizing speech.

Likewise, wearing a seatbelt is an action so requiring seatbelts is compelled speech.

And words are speech, too. So requiring car owners display their license plate is compelled speech.

In order to bring the job market closer to "perfect competition", thereby making it more efficient. One of the features of perfect competition is "perfect information":

"In economics, perfect information (sometimes referred to as "no hidden information") is a feature of perfect competition. With perfect information in a market, all consumers and producers have perfect and instantaneous knowledge of all market prices, their own utility, and own cost functions."

Posting a salary/pay range is no different than posting a job position and a location.

No plumber in Indiana wants to apply to a job that ends up being an opening for a brain surgeon in Botswana. Why should companies be able to waste time with wages that are below what applicants are looking for and only tell them after the seventh stage of interviews? It’s disproportionately advantageous for corporations.

Because markets are distorted by unequal access to information.