Bukkit was bought by Mojang. Bukkit dev team wasnt aware of this for years, when they found out they closed the Bukkit project because of butthurt. They issued a DMCA takedown on their own project to get all forks closed as well (classic case of "its my ball, and i dont want to play anymore"). The DMCA was filed on the bases that CraftBukkit (and all forks) were distributing GPL licensed code (craftbukkit code) along side non-GPL licensed code (mojang's code). Since the GPL strictly forbids this the DMCA is legit and all forks were shutdown as well. All versions of CraftBukkit (and forks like Spigot) of versions 1.7.x and below all fall under this redistribution law (as stated in the GPL license), making it illegal to distribute in any way (aka, you can't legally obtain a copy of those jars anymore). This is why Spigot responded with 1.8 using BuildTools. BuildTools allows Spigot team to distribute the GPL licensed code by itself, which is perfectly legal under the GPL license and is not effected by the DMCA takedown. The GPL and non-GPL codes are downloaded from different sources and combined on the client's PC with the help of BuildTools. TL;DR: Versions 1.8.x and above redistribution is perfectly legal. Versions 1.7.x and below is illegal to redistribute. Because of this, a lot of projects have chosen not to support 1.7.x and below. Get over it.