As a fellow tank, let me just say I feel you. I really do.
I used to be the go-to guy for years. had an alt that needs equip? Ask me and I tank some dungeons for you. I even help you get your nhc/hc raid run. I have equipped dozens and dozens of alts over the years.
But when I had an alt that wasn't a tank or heal, it would be nigh impossible to find someone to help me.
Eventually, i stopped doing that. The great thing about being a tank is that people need you. An over the past 10 years, my friend list has grown. I now have my premade m+ group, and run my keys with them. I do not help other people gear their alts anymore. I only do that when i have an alt lined up, and then I communicate my expectations clearly, like "I will do five dungeons with you, but make sure to repay the same for my alt <insert name here> by the end of this week". I'm sorry if thats inconvenient for people, but after ten years of gearing other peoples alts, I'm done.