I think you'll find it's not that they can't make ends meet, rather they've made a priorities choice.
Which has absolutely nothing to do with the RM - or more correctly - naval service budget in the UK. It may have escaped your notice, but one is a large all arms organisation in the US, the other is essentially a light infantry raiding force in the UK.
Do they not do apples & pears comparisons where you come from?
The U.S.M.C. is about the size of Britain's entire Armed Forces and are held in great esteem in the U.S. a lá the Royal Marines are here.
If they as you say are making a priorities choice then we will be doing the same.
It is a fact that new equipment is swallowing up Defence Budget increases and more, something has got to give.