American manufacturers never cared for rallying, and very rarely fielded works or semi works car in their championship. Of course one thinks about Ford, but that has always been Ford of Europe and then M-Sport. Entry lists that are small or low quality show lack of interest and that rallying is a super niche sport over there.USA is Rally TVs single biggest market. And if attracting manufacturers is important, being there helps. Entry lists have nothing to do with it.
But, the geographical spread of ARA National is much larger than ERC and has more regular starters. And the entry lists of the ARA rallies are split between the national and regional championships - which also each get regular starters and still cover more ground than European countries like Latvia, Estonia and Croatia - and local drivers.
Add also the early collapses of AAA and ACA allowed a free market for motorsport sanctioning, so there are all sorts of rally racing, rally sprint, auto-whatever series similar to rally for legal or whatever reasons. Not all are affiliated with ACCUS, the FIA member. Motorsport is huge there, taking WRC would help ARA/USAC become the focal point, which could also concentrate entries.
I compare ARA with other national championships. One would expect that if big USA was a powerhouse or potential powerhouse for rallying, their entry lists would dwarf the ones of the small European countries. If you sum up national and regional, I guess they sometimes reach the number level of certain European countries, the quality of the cars... not so much.
Plenty of European countries have a gigantic amount of regional rallies and trophies, so I don't see those other American seriers as an "excuse" for USA.
I think NASCAR is huge there? I would imagine Indycar, F1 I don't know because I don't care... rallying isn't, for what they show and what they've always shown in practice.
If RallyTV's biggest market is USA, they can continue watching on the app like everyone else who doesn't have a WRC round in their country. The interest certainly doesn't reflect in the quality of their national championship entries, nor I expect many of those fans to travel across the country to Tennessee to watch 7 top category cars and few Rally2.