There are a couple aspects that probably explain why streaming services are popular here in the US:
1) Geography. Americans tend to be spread out and have a much larger mileage distance to commute. As an example, I commute 38 miles/day each way to work. My father is still commuting 55 miles to work each way and has been for near 4 decades. 40-60 miles is about the usable range of the vast majority of FM stations here…unless you’re dealing with 100kW flamethrowers on a high tower or mountain ridge. That would be comparable to the “national” services in the UK/Ireland (BBC services/RTE/ClassicFM/etc). From my experience, most independent local radio stations in the UK/Ireland are fairly low powered/low height, and would be equivalent to our class A stations (or less). So usable range is 10-30 miles out for most of those stations. With streaming or satellite, the coverage is far more universal.
Interesting thought, but not the reason.
In the early 30's when the FCC was formed, a number of senators were afraid that if radio stations were allowed high power, the coverage would exceed the circulation areas of city newspapers and thus be a bigger political force than the press. And if companies were allowed to own too many stations, they could influence national politics more than print media, too. So caps were put on power and ownership.
Of course, back then the only places in Europe with private radio stations were Luxembourg, Andorra and Monaco. So the development of radio in Europe was vastly different.
Ireland has about the same land area as Indiana; no single station covers all of that state and, in fact, there are multiple larger markets including the Louisville and Chicago suburbs, Ft. Wayne, Indianapolis, Terre Haute and others that have their own set of FMs with good facilities. Even the national services in the UK, Ireland, France, Spain, Germany and others use dozens if not hundreds of transmitters and boosters to get national coverage.
2) Regulation: In most of Europe/UK (and many other countries), radio formats are regulated. One couldn’t decide on a whim because it would make the company more money to make a major change to a radio format. It requires (at the least) paperwork and regulatory approval to do that in most countries. What that means is formats can (and frequently do) come and go from local US airwaves based on potential financial success, not based on what the government, commissions, or even the local community desire. As an example, rock and sports talk are by and large low-ratings formats in the US, but the money made off of it by direct response ads makes it a successful format to the point that it’s a very common format in most towns.
In plenty of nations in Europe, the regulation is hardly any more severe than in the US. Spain, Portugal and Italy are very free, and even the private stations in France, Germany and Austria have considerable leeway in programming. Others, like France, England and Poland are a bit more restrictive but stations have quite a good opportunity to determine formats and operations.
Rock and Sports don't live off direct response ads to any significant extent; many won't even sell that kind of account. Direct response is more of a TV revenue device, since most TV shows have fixed commercial breaks they have to fill so "PI" (per inquiry) ads are used to occupy the time.
Sports is a highly profitable format because it delivers adult men efficiently. While such stations don't generally dominate the 12+ audience data, they do show amazing strength in 25-54 men and they sell based on those high ratings. There are lots of advertisers who sell specifically to men who don't want their budget wasted on stations that deliver women.
There are different kinds of rock formats. Alternative radio is in trouble because the music genre is in trouble. AAA is too old for commercial stations, so is mostly heard on non-commercial ones. Classic rock is big in ratings and revenue in most markets. And very few run direct response ads in significant numbers.