There are numerous reasons why officials are in short supply. A few of them here...
1. Pay is low, relative to time spent. Fee increases are typically well below the increase in cost of living. Cost of Living has exploded in my area recently. School funding increases at a steady clip (see my property taxes as proof). Officiating increases are typically in the 1-2% range, if any.
2. Schools' insistence on overloading their contests on only 1-2 days/week. A balanced schedule would allow those officials to be utilized more effectively. Not enough
VB refs on Tuesday/Thursday...most officials sitting home on Monday/Wednesday/Friday. Brilliant! I've personally seen 80 slots on a Tuesday, with less than 5-10 slots on the Monday and Wednesday.
3. Abuse from coaches and spectators. Many quit during the sensitive time when they really aren't very good and are learning. Administrators find it completely acceptable to have their coaches badger officials (even rookies at a freshman or junior high game), then wonder why these newer officials quit after their first or second year.
4. Perceived unfair path forward. Many associations are operated and controlled to the benefit of the select few. After a while, the newer officials see that their input isn't valued and advancement will be difficult due to external factors (not simply their competence). Opaque post-season selection and ranking processes are devastating to the health of an officials association. Most everyone is OK with not moving up the ranks, if they believe things are transparent and fair. If things aren't transparent and fair, officials quit at an alarming clip.