Here's something to consider. Any community should strive to welcome new members and be friendly to newcomers. It's not farfetched to say that new twinks in this bracket will make a 79 first, for 3 reasons - x9 is standard twinking for most brackets, it's much easier to get BiS gear from running normal dungeons than to depend on weekly Sunwell lockouts, and 79 is simply stronger than 70 for reasons well known to all.
So what would be great would be if the community of existing guilded 70 twinks, when they spot a new 79 twinked player, reach out and say something along the lines of "hey, nice gear, have you thought about X trinket instead, etc" and then segue into "by the way, if you plan on playing this bracket a lot, have you considered making a 70 twink? we do raid, duel events etc?" That's the attitude that will make me stay in the bracket and put the effort into making a 70 twink.
Instead here's what my experience has been on my 79s (I only started twinking a couple of months ago): /spit from both enemy and friendly twinks, whispers from my own faction horde twinks saying "79s suck, you suck, blah blah" etc. Only once has someone said anything remotely friendly. Yes, once in 2 months, whereas the negative experiences have been in the double digits. There's also the indifferent/dismissive attitude I see in this thread as well.
I'm sure the 70 community has nice people too, but so far I have been rather disappointed in it as a whole. Zero desire to make an objectively weaker twink that takes a long time to gear to BiS just so I can join the community after my experience.
I do hope the overall attitude improves, unless I've simply been extremely unlucky and just keep running into rude and angry people all the time.
Edit: I play EU Horde, in case it's relevant.