I can't imagine moving my comic solely to Tapastic!
My website is pretty simple, but it's where my comic is meant to be seen, honestly. Tapastic makes it awkward to post extra content and organise side information and engage outside of the comic pages, while on my website it's easy -- I have a whole gallery of silly extra comics, old vote incentives posted along with my comic, an FAQ, a cast page with extra info on my characters (and silly things like birthdays and theme songs). My website feels like I invited people in to meet me so I can tell them a story; Tapastic feels like I shipped my artwork off to some gallery where it's going to hang on a white wall -- I feel very separated from my work. I'm glad to be featured there, and I can mill around and engage the people there in that gallery, but it's not my space, and it doesn't feel like my space.
Also agreeing hugely with Kayke on the benefits of having your own snazzy URL!
Social media, word of mouth, collectives like ComicRocket and TopWebComics -- the same sorts of ways webcomics were found before Tapastic was a thing! Back in the day it was places like Deviantart or putting a link to my comic in all of my forum signatures (I used to be on a D&D forum where I posted sketches of my adventures, and a lot of people who enjoyed those checked out my work) -- and now it's more places like twitter and tumblr. It's the same as here; you participate in a community and engage with people!
People don't have to make a Tapastic account to comment on my website or subscribe to my RSS!
In general, there are a lot of people who don't like Tapastic -- whether they find the system confusing or don't like the layout or find the lag awkward or just don't want to make an account. For those people, the personal website is a lot more accessible!