That depends if they did not have the right developers, but why take time to start from scratch when they have something to work with?
Well, we almost know for sure about the first part: they don't have the right developers. Browser development is not Comodo's core competancy. If it were or they had the right developers, they *would* build their own browser. But the fact is they can't or don't have the time or developers or resources.
Haven't you seen the less than stellar job CD is doing trying to keep up with Chromium releases with strange issues and regression problems? They are trying to keep up with Chromium where all the real developments are. Do you think Comodo's doing this by choice? They are doing this out of sheer necessity or else they fall behind every 6 weeks. Do you think the CD developers are happy? They are taxed, tired, and extremely rushed!
This is all because the 90% of CD's core functionality relies on software they don't control, and what's worse, changes/improves every 6 weeks, and CD users know this, and even post here rushing CD to keep up with the latest Chromium. If Comodo had the right developers and resources, they *would* take the time to start at least with a codebase they could control.
(Of course, CD could control the current Chromium code they have now, and try to do their own further development from that. But that's the crux; they don't have the developers or the core competancy.)