I think what you've seen here is not a lack of Hendrix fans, but more an understanding that this is a battle of the bands, not a guitar player contest or an individual legacy contest.
Look at it this way, using an analogy from the world of hockey. This year, Alex Ovechkin will likely surpass Wayne Gretzky as the highest goal scorer of all time. At this moment, as I write this, he is only 12 goals away from breaking the record (there is a Capitals game on right now, so that number could change as soon as I submit this post!). However, the Washington Capitals, as a team, have only won a single Stanley Cup. This year, up to this point, the Capitals are doing well. But, they could still slump and do very poorly, even though a player on the team may break the world record for goals scored.
So, the motivation is NOT to minimize Hendrix's contribution or legacy. Many of us recognize that very much. But, in looking at this as a band vs. band, the tables turn in ZZ Top's favor in many peoples' opinion.
EDIT: The game is over. Ovechkin scored. He is now 11 goals away from surpassing Gretzky. However, the Capitals lost. They have now lost three in a row, so they are in a bit of a downturn. But, Ovechkin could still easily break the record. It's well within his reach.