The Spider work for the "power" that wants to destroy everything the rest of Rokugan believes in.
Who exactly has a reason to support that?
Everyone who thinks Order must be maintained over Chaos, and that respecting the Spider in a courtly honorable fashion maintains Order and thus does a better job of protecting what Rokugan believes in (which is Order) than allowing the rules of the system to break because you really, really, reallllly dislike someone the rules say you should treat with courtesy.
Stop looking at this as "giving things to the Spider" or "doing things for the Spider" as if it is unfair to give them things or do things for them. That's nonsense. It's nonfunctional. That model has completely died, we are not in a mode where every prize given to one side is a prize not given to everyone else -- if you keep seeing it that way you are wrong.
The only things I am interested in giving to the Spider are things that allow the Spider to serve the entire setting better. The entire setting is served better if the Spider can be the Vegeta of Rokugan, and if people have to play nice with them at court because that is what maintains Order (and if the Spider must play nice at court with people they would rather be murdering because that is what maintains Order). It allows much more interesting personal and Clan-scale conflict. Spider are carrying a lot of weight because they are antagonists and antagonists are really, really important to the functioning of a story. Forcing the courtly clans to interact with them, sipping tea through clenched teeth is not something that benefits the Spider at the expense of the courtly clans, it is something that benefits the courtly clans by involving them in the conflict and giving them more opportunities to show off their personal and clan identities by placing them in situations where they are tested. In-character, Spider at court is bad for all of the other clans. Out of character, Spider at court is much better for all of them. Right now, we want to find otu the best out-of-character state, and then come up with the proper justification to arrive there.