[Tiger Fan]

If I am understanding you correctly you say each expansion team folded after 1 season. If so, do you have historical minor leagues included or automatically expand league checked in the historical tab of league setup? If you do then that is likely why as historical will follow real league alignments with minors enabled.

Meaning that teams that did not exist would not be around when you advanced to a new season. So what might be happening is the fictional evolution is creating expansion teams but the historical progression is deleting them at the end of the season because they did not exist in real life.

So by having all historical options all enabled it does things that happened in real life like move the Browns to Baltimore, but the same process that checks for real major league evolution I believe immediately after the World Series is completed is deleting the expansion teams that were added by the fictional world evolution option.

It won't stop the expansion teams from being created because that happens after the check for team setup for the current year, but it will delete them after one season because they should not be there when following historical progression.

EDIT-
The work around is uncheck the option (I believe it may be called automatically expand league) in the historical tab. This will allow those fictional expansion teams to continue to exist but the trade-off is if you want the Browns, Braves, Dodgers, Giants etc to move in the 1950s you need to do it yourself manually.