It's a give and take, so I don't think it's sad at all. Bands who want Blaze to guest aren't doing it just because "oh that would be cool to have him do it." Yes, that's probably one reason, but they're mainly doing it to attract Blaze's fans to their music in hopes of gaining new fans, and he's likely very affordable for a band that hasn't broken yet. Also, artists have to eat too and deserve to be paid for their work, so no, he shouldn't be doing it for free.
On top of that, it's not like Blaze is financially set for life. He's said many times in interviews that he has a small but dedicated fan base that allows him to do this for a living, and even post-Maiden, he's had to go out and get day jobs from time to time, like the wheelbarrow factory he worked at for a while.