Personally I don't think the game is "monotone" due to "grinding" and "mining" gold at all. There are sufficient quests and dungeons do reach the level cap without grinding even once.
If the reason for monotony is reaching the level cap and clearing the dungeons, then I feel adding features that involve people doing nothing for prolonged period of times (I always find fishing in MMOs very monotone) isn't going in the right direction. In addition, while it may seem simple, adding fishing is something I can't just implement and "leave it like that" - if I start doing that, I have to keep adding content for fishing as I add levels - it's a short term "solution" to keep people busy a bit more, with a lot of additional work in the long term. I already should be adding in more cooking and alchemy recipes.
I rather add proper content, but that needs time - especially considering that over 99% of the content is done by me, and additional help virtually doesn't exist. It could be so simple: you have 5 hours in the evening you don't know what to possible do with, and feel you're just "grinding"? Write a quests, draw items, I have been accepting everything since forever, but gotten very very little. These would all be added in, bamm, instant new content and new things to do. Writing quests and drawing items is getting quite close to making your own game without having to type a single line of code or providing the infrastructure. What instead happens is that virtually no one provides anything, leaving the overwhelming bulk of work on my shoulders, and leaving me to feel that I could always do more, more and more (but I'm already working on the game hours each day). Sure, some parts are best done by me: scripting encounters, adding code to the server and the client, there's no real alternative to that. Drawing items, writing quests, or making maps is something anyone can do. What happens in reality though, is that I have to do the things only I can do, and also the things everyone else could do. Nevermind the fact that everyone providing something had been compensated.
But we've been down that route already. ;)
Yes, I do realize I do get some content help every once in a while: however they're part of the sub-1% of the work done. When I get a tiny bit of help every 2-3 months with something I could have done in 20 minutes myself, then it's hard to ignore the 99%+ I am doing. It's a tiny, tiny drop in the bucket; so tiny it almost doesn't matter anyway.
I hope this also answers the question "why not Paw'D". :)