They don’t care about ‘upselling’ - it’s just that they only really care about the orders that are at least in the tens of thousands of units (or for the Broadcoms of the world, hundreds of thousands) per year, and ongoing.

If you even promise to buy a few hundred a year through a business, it puts you in a different category and everything gets much easier, but you usually have to go via a distributor (Avnet, Future, Arrow etc.). But if you’re big enough (the hundreds of thousands + qtys) these companies will actually send dedicated support engineers to work with you and help you integrate their parts into your product.