(3) watching Alberth trying to fix this issue in OpenTTD
Expanding on this a little. The game has some X number of industries per 256x256 area. This number slowly rises by 1 or 2 each decade or so (unless eg default industries are closing a lot, which is a sign you're not able to manage the current amount, so no point in further increasing it).
As a dramatic example, assume we have 4 industry types, and 80 industries. For simplicity, each has the same chance of appearing, so theoretically, you'd have
20 A, 20 B, 20 C, and 20 D.
Now one new industry-type is added, again with the same chance of appearing. If industries are sometimes dying, you'd end up with 16 A, 16 B, 16 C, 16 D, and 16 E, ie each of the 4 existing industry-types gives 4 spots to the new industry-type. Depending on the rate of closing, this can happen quite fast with default industries.
In FIRS, the default is not to close industries. As a result, the only feasible balanced outcome is 20 A, 20 B, 20 C, 20 D, and 20 E, which at 2 new industries/decade/256x256, takes 20 decades at 256x256, or 5 decades (50 years) at 512x512. If you add more new industry-types during the game, things slow down, as all new industry-types are competing for the same very rare new spots.
In other words, for effective new industry-type introduction, you need industries closing down, so they can be replaced by a newer type. Without it, your game has ended before they are properly added.