Don't rely on the forums alone to advertise on. Use social media, grow a following on social media too, try livestreaming, do fun extra things to get people excited and interested in your art, fan art, guest comics, art requests, try paid ad spaces, trial and error and find what works best for you.
Yes, time is a part of it. It takes a lot of extra hard work to gain attention and build a readership and that does take time.
It's good not to be concerned with the numbers and subs and just create. However posting on Tapastic requires LOTS of self promoting. It's slim chances these days, with so many creators now on the site, to get featured on the front page in any of the sections. It take doing more through promoting in multiple locations and doing extra stuff to get people interested.