Newbie question - number of bikes per team

Hi, there! Longtime Formula1 fan here, have just gotten the season pass for MotoGP and caught up on the first four races of the season. Most of this seems pretty straightforward, and even familiar, but I am curious why KTM was able to run three bikes in Spain? Why did they only start doing so in Spain? Why wouldn't other teams?
Submitted May 08, 2018 at 08:01PM by emeksv https://www.reddit.com/r/motogp/comments/8hzbfh/newbie_question_number_of_bikes_per_team/?utm_source=ifttt