Where are the thousands of Gmail competitors?
The reason they don't exist (or they do exist but you never hear about them) is that you'll have to pry Gmail from people's cold dead hands. Firstly, Gmail is an amazing product, and it would be really, really, really hard to do better. Very few teams can attempt such a thing, certainly not thousands. Secondly, even if you build a better product, it's extremely unclear how it would be enough better to get enough people to leave Gmail.
Word processing and spreadsheet competitors?
Exactly the same reason. Microsoft Office is an amazing piece of software, and it would be immensely difficult to do better. Furthermore the barrier to entry is huge -- word processing and spreadsheet software that can effectively compete with MS Office would take decades to build.
There is something to be said for competing with Google's online office offerings (and I know some really smart people who are doing just that), but again, it's not as easy as it seems.
Where is a better DabbleDB?
DabbleDB didn't work as a business. That's why there is no better DabbleDB -- there is no market for it.