Mine does that.
I've had to refuse much the same offers you did, cash, home, car, a business of our own (that he would run so I wouldn't have to work and be able to follow my passion instead), wicked expensive vacations - you name it, he offered it and I got confused/scared/offended by it.
In time, I learned to at least accept the "smaller" things that still allowed me to look in the mirror in the morning. Still way too costly for my taste, but fancy dinners and jewelery at least weren't AS ridiculous as some of the rest and being allowed to give them to me made him feel better.
That said, his black AmEx is burning a hole into my desk drawer and will never be used, no matter how often he may insist I "treat myself".
He was raised to believe he's not worth more than what's in the bank, that no one's ever going to love him for anything other than what he can do or buy for them. It didn't help that every woman he got close to in the past absolutely confirmed that theory, and he's WELL out of his depth, scared and very uncomfortable with the idea that some people may be different.
In his mind, he himself is "not enough", because that's what he's been told all his life, and teaching an old dog new tricks really IS as hard as the old proverb claims.
Another aspect to it all is that of Chapman's "five love languages" (you might want to google that if you're not familiar with the concept, might make some things clearer).
That theory isn't really backed up by science, but relatable enough.
Chapman's theory says that there are five ways people express love: gifts, quality time, words of affirmation, acts of service and physical touch.
According to the this, everyone has a primary and a secondary "love language", and if there is no overlap in yours and your partner's, that's when sh*t gets confusing.
Not impossible, but confusing, because it'll take some effort to understand and be comfortable with the way your partner expresses love.
There are numerous resources available online that'll explain it much better than I could, but the "language barrier" and the toxic thoughts planted in that gorgeous head of his long before my time are the issues I'm facing with my vet when it comes to the kind of problem you're having with yours.
It's confusing, it even seems insulting ("WTF does he think I am that he's trying to buy me!!"), and if it's not a way of thinking you're used to, it takes quite some time and work to get there, from both sides.
You sort of have to meet in the middle, and getting there takes both parties through pretty much uncharted waters - but it's not impossible. :)