It was built for a Unity WebPlayer, whose support has been discontinued. Most of my games have been built for that, and a lot of them are sadly now defunct.
Restoring them is sadly not trivial. Here are the steps involved:
- Finding Source-Code (my good filekeeping makes this quick)
- Re-importing into Unity with WebGl-Settings. Depending on the size of the project this might take up to 1 hour
- Adapting code to new standards, which is fairly straightforward, but has the potential to take up a lot of time
- Dealing with Plugins & Libraries. This makes me happy I was anxious in the past about overly relying on 3rd-party-elements outside my understanding, and I was totally right. A lot of old plugins have now non-accepted code or just stopped working. Even if they are still supported getting the newest version and integrating them would take a noticable amount of time. Not to mention tools which might have changed their pricing and have thus become more expensive to acquire. This can become very time-intensive.
- Checking everything in the game still works correctly
- Checking everything still works after building. Unity WebGL-Builds sometimes produce issues not found in other builds, and this needs to be taken care of
At best this entire process takes 2-3 hours. At worst (as it was 6 months ago for another game) it took me a month to figure out a super-slow publishing issue.
This is why it is infeasible for me to re-release all of those old titles, even though I would love to.