Because that's the one that was originally blacklisted, and is currently blacklisted. Mojang can't fix the SRV bypass thankfully.
We use something called an SRV record to point all traffic from a certain port, this case it's 25565, to a given subdomain.
Pretty much, except you can keep connecting to mc.ecocitycraft.com or ecocitycraft.com and it won't affect you in any way. So don't worry about it.