If the only option you had was group games on one site then it is understandable why you don't understand why one-on-ones are better. It is truly rare for a group game to go faster than a one on one. If you are interacting with more than one person it is usually considered rude not to give everyone a chance to respond before posting again... you can, but eventually you will leave the slowest player behind and frustrated... they will quit. You will also miss the opportunity to take the game in a direction that involves everyone's input... not just the fastest posters.
Take for example the group game I am in Beyond Hogwarts. I have not had the ability to respond daily or even every other day. Not even the game owner has been around to post. Yet there are a few who are capable of making several posts each day. Because of this there is a time difference in where we are. It frustrates me because the slower posters won't ever be able to catch up and get the experience out of the game that role playing is supposed to bring.
With a one on one... all you have to do is wait on one partner. When they are in a good position to post your game is going to move. If they are not then at least you know you are not going to be in a position to wait on more than one slow person. Even more so if a person has to stop gaming for a while then you both choose to pick up the game again when they come back. When people leave groups games and you do not have a good gm... the games usually die.
Now to address the m/m problem. There is a disparity between those players who enjoy m/m that are 'top' and 'bottoms'. It is very frustrating for those of us who will top because most of us also bottom. So if you think it is simply hard for a bottom to find a top... you are competing with tops for the other tops. And even if someone who tops has a game opening... if we are topping for every other game (or most of our games) then we are less likely to pick up another game where we are yet again... topping.
If you consider yourself a 'bottom only' person I would really like to encourage you to expand your horizons and volunteer to top for another bottom. You may find that you enjoy it... you may not but it will result in you being able to play more games and it will take some of the stress of those of us who to top from having to turn people down because we don't have available game slots.
Most of us really do feel bad about turning people down. And though I don't turn many down... the more I take the longer everyone waits for my posts. So I get to feel bad about turning people down and making my partners wait for a response