The thing about that is Riot wants people who are self-sufficient and have the money to help establish the ecosystem, it seems. To compare:
TSM is sponsored by several major organizations.
CLG has the same deal.
Cloud 9 also has major sponsors
Team Liquid feature much of the same.
The outlier here is Echo Fox, who don't seem to have any sponsor. They do, however, have the (pretty decent pockets) of Rick Fox backing them. Comparatively, to the ones who we know are out...
Echo Fox has six sponsors but you ned adblock off to see'em.
P1 only has four sponsors, only one (Twitch) being a HUGE org.
I legitimately couldn't find anything for Flyquest.
IMT has three less-than-large orgs backing them.
To add to this, IMT is backed by VC money. VC has a tendency to pull out hard n' fast when things don't look good. Say Immortals botches something in the LCS. Suddenly Riot has a financially weak org in the ranks and has to pull them up as much as possible.
All things considered, it's a shit situation especially considering how well-liked IMT is in both the scene and from the perspective of the players. Considering the decent friendship IMT has with Riot, I'd hardly say this was a spiteful or easy to make decision. All we can hope is that IMT can one day rejoin when their pockets are a bit deeper.