"Support" is a pretty nebulous term here. I don't think anyone other than WotC is expecting their 5E ruleset is going to keep the lights on all by itself.
For Kobold Press, ToV is an adjunct to their settings, adventures and splatbooks, allowing them to create for it even if WotC goes crazy and announces a 6E for 2025 that's completely incompatible with what's come before. But barring that, they don't need it to have a higher profit margin than any of their other books.
Similarly, Cubicle 7 appears to be treating their 5E books as supplements that will be used by DMs using any 5E system.
This is just a different flavor of third party companies creating supplements for the game. It's just that these products, in particular, can potentially be used to replace WotC's system, if one so chooses.