It's interesting given the roster cap imposed by NCAA rules.

By the first game of the regular season (February 14, 2020), a Division I baseball team's squad size cannot exceed 35 players. Up to 27 players can be on scholarship in a given year, and if you are on scholarship, you must be included in that 35-man limit. Those 35 players are the only ones who can practice the remainder of the season, so if you were carrying 50 players in the fall, the 15 left out are effectively off the team at that point. (This roster-cap has been around since 2008, in large part due to baseball's APR issues caused by huge rosters encouraging rampant transfers.)

Even though there's that forthcoming roster cap hanging over your head, there are still reasons why you'd want to carry extra players in the fall: depth, players coming back from injury, uncertainly about the last 2-3 roster spots, etc. I think it's crazy to carry 50+ players on a baseball team because I don't know how you effectively run a practice with that many players, but whatever.

A few rule changes the past two years have made the 35-man limit a little more flexible. As I said above, if you are on scholarship, you must be included in the 35-man limit. Previously, that applied even if you were injured or transferred before the season. You could get a waiver in some instances to replace a player, but you'd often have cases where your 35-man roster was effectively trimmed down right off the bat.

Recent rule changes now allow a team to replace a scholarship player's spot on the 35-man roster if: 1) He suffers a season-ending injury prior to the first regular season game; or 2) He voluntarily quits the team prior to the first regular season game. In both cases, the player replacing the old one must have been a walk-on who was already with the team in the fall (no midyear additions). Given the new flexibility to squad size, it makes sense that teams are more open to additional walk-on opportunities in the fall.