Companies this size have serious issues with the left hand not knowing what the right hand is doing, or worse, not knowing if the right hand even exists.
You had a somewhat successful interview. There are 3 jobs and 50 candidates. Some are clear "no"s, a few are clear "take him to the next level"... but there are also ones stuck in the middle. Good enough that they could go to the next level, but only if the eight people in front of them wash out. That's you.
In addition HR may not be sure if there really are 3 jobs (there can be more or less), and they are also recruiting at other events and are hoping that someone stronger than you turns up.
And then weeks pass and odds of them needing you get much smaller, but never quite fall to zero. Then months have passed and it's not worth their time to review the dozens or hundreds of people they've kept in the pipeline waiting.
In addition, this is a big process and "they" is more than one person. It's unlikely that the person who told you that you did well even knows whether or not you've made it to the next level.
Edit to add more info: Small companies typically one HR person in charge of the entire process with a well defined number of jobs and candidates. My HR person is matching thousands (yes, really) of candidates to scores of jobs.