Some brands choose to put the endorsement tag on artists and give them free gear in order to increase their visibility. For example... if Flea is a popular bassist for a popular band, and Modulus keeps him playing their gear, then fans and musicians see this and often will want the same gear to match the tone/style. Usually it's the luthier and/or manufacturer that approaches the artist to offer that partnership.
Unfortunataely, many musicians with decent level of skill have been spoiled by this concept, and feel like they are entitled to an endorsement and free stuff just because they know how to play and happen to play in front of big crowds, and cop a serious attitude if they don't get it. It's a pretty sad display.
I agree with Tim on this 100%. If you like the gear that you use, buy it, plain and simple. If the people who make the gear that you like to use offer you an endorsement or just choose to give you free stuff ,that is strictly at their discretion. No musician has earned the right to free stuff, and you're only entitled to what you earn by the sweat of your brow. Chumps looking for handouts can kick rocks.