It's a tier reward though, as it's listed as such
we also don't do groupings of rewards, just due to not having enough slots in the game to fit everyone in.
For example, for the $10 background tier, there's only a limited amount of space we can put names, given how they're going to be put in the game; this means that if we gave that to everyone who did $20 or $30 or etc. tiers, we would quickly run out of room and have to turn people down, including people who specifically pledged to it and really wanted it vs. people who just wanted it on a whim because it came as a bonus to their higher pledge.
Additionally, some of the pledges cost us money (ex. the $20 pledge for voicepack we pay out 100% to the voice actress for Talia/Vie with, and the music tier we pay 50% out), and for the $30 tier databanks, we pay other voice actors to do those.
Adding onto all of that, the full game effectively is going to be sold for $15-20, so getting the game at $10 is already a good chunk off of the game's retail price.
So if you factor in the above two examples, you'll find that we're actually effectively losing money on the $20 and $30 tiers and putting the game on sale for all tiers as well, and if we gave people a bundle deal on tiers, we'd be in the hole pretty fast financially (as well as again running out of room on things like the databank/background tiers).