NCAA rules give you five years to play four seasons. The fifth year is the redshirt, which means you can be part of the team but not play in games. Sometimes if a kid gets injured, the NCAA will give them a sixth year -- a medical redshirt -- but it's actually pretty rare.
The other part of what you're saying is that a coach designs their program for a certain number of players both at games and practices. Practice times are usually limited by rules, so if a coach has 15 players on her team, she gan give them ll more instruction time than if she has 20. Or 25. So even if we keep extending eligibility, the logistics of these expanding teams will be difficult, too, both at the high school and college level.
So if an entire team was prevented from playing in the spring of 2020, why can't the entire team use "five years to play four seasons"?
I do realize this is hard on everyone including the coaches. Every person has their own version of what they want to see happen. Sometimes for biased reasons. I am trying to look at it from all sides. Personally, I do not think any solution is going to satisfy everyone. But how can you make it the most fair for as many people as possible?