I'm going to reply with my own personal observations about what's been happening - note that my goal is not to offend anyone but to point out certain behaviours/actions/etc.

First of all, Vazkii and the FTB team do disagree on a lot of decisions relating to inclusion of Vazkii's mods in various FTB packs - this has been going on since 1.7, really. The issue is a lot more complex than "FTB has made bad decisions in Beyond!", really.

Second, people fail to realize that, as FTB is no longer the underdog fighting against Technic, but the biggest modpack brand in all of Minecraft, they are under far, far more scrutiny and people except far more of them than they do of other, smaller, less organized teams.

Third, many modders have been privately deeply upset about FTB's decisions - this isn't just Vazkii, really. I won't name names here, but the sentiment is generally visible if you know where to look and the "FTB: Beyond" rallying is definitely amplified by the annoyances accumulated over the years. I don't think any modder wants to have their mod's vision misrepresented in the most popular modpacks.