Was reddit just more convenient? Do people not know about this site?

I would agree with both of those being a big part of the reason. Reddit has been active since 2005, and has millions of users, while SaidIt is still rather small (less than 50K users, if I remember correctly). If you venture out into other subs, you'll see the same names over and over ... there just isn't the volume of users here that Reddit has.

But also, Reddit fills a gap that other sites haven't really picked up steam with yet, which is mindless browsing and advice subs. Think about r/aww or r/tifu or any other popular sub, people can click-click-click and upvote a cute cat pic when they're bored, or engage in some armchair psychology with other users. Those subs have nurtured a specific kind of culture and that takes effort, effort which other sites (like this) are still growing into.

Another reason is that SaidIt, and really all Reddit-alternatives, get painted as "alt-right havens for nazis and anti-Semites". Redditors like to pretend deplatforming works to "get rid of hate" and "fracture the groups so they can't find each other anymore". While there is a little bit of truth in that, what they willfully ignore is that anyone who is banned, be they right or left, nazi or hippy, will continue to seek out others with the same experience. Some users choose to make alt accounts on Reddit and antagonize them further, while some choose a new site and leave Reddit behind.

When you deplatform all the nazis, they don't blink out of existence ... they find <newsite> and gather. When you deplatform the next group, they remember hearing about <newsite>, and even though they don't really want to hang with nazis, they give <newsite> a chance, figuring it's gotta be better than the last place at least. And slowly-but-surely, that's how <newsite> gains traction and grows into something better.