Chicken and egg to some extent. Monero is small and relatively unknown for another. Okay, its pumped a bit, and is now a reasonably solid #8 by market cap (not the only ranking of course). That means there are 7 ranked higher. A few months ago it was #15 or something, so even more obscure. Finally there are tech issues that have been resolved only recently or are still being resolved. For example the whole payment ID concept was a royal pain the ass for integration. It is handled now by integrated addresses, but that is recent. Still, there needs to be more work on the APIs for integration. Likewise, until recently you needed gigabytes of memory to run the wallet. That puts off anyone running on a cheap VPS (often limited by memory more than anything else). The command line wallet puts some people off on the user side. GUI's exist, but they are third party and not integrated. None of it is easy -- you have to be quite motivated to overcome the barriers. We have to reduce them. It is happening, but as a process, not an event.