Sponsorship is really just a promotional agreement; this idea of sponsorship having to be "earned" just makes me chuckle. There are no free lunches, and if a given company is willing to part with either product or money or both, you can bet that they aren't doing it out of the goodness of their corporate hearts, but to gain something from the transaction.
That having been said, different companies have different business plans/business models/advertising strategies, but the end goal is usually the same: to have their product or service seen in the most favourable light possible, so as to generate sales and thus, revenue.
When I think about it, offering a pro or club driver free or discounted equipment is probably a very efficient way of promoting one's product.
Let's take engines for example. Let's say that BRAND X has a mill that retails for $300, and they want to get the word out to get as many people as possible to buy the BRAND X mill. The engine itself probably costs $70 to fabricate, parts & labor included, so even if they flat-out give a dozen of them away, those dozen BRAND X-sponsored runners will probably be seen by 800-1000 people each (conservatively), over the course of 6 months, so roughly 12000 people reached in total.
Of those total 12000 avid RC-ers, maybe one in ten will actually buy that mill, so 1200 mills sold... With less than $850 out-of-pocket. Granted, I've grossly over-simplified the matter to make my point, but you get the jist of it: if a company "gives" someone something, they're getting something back in return
