The key issue is Rangers still want Opening Day 2020. There's a handful of teams that have conceded March/April/May, but Texas and a few others are still telling people to hold onto their Opening Day ticket for "new Opening Day".
So that's why they are trying to drag it out. If they can get an Opening Day 2020, then you can pitch that to season ticket holders as a reason to not get a refund, keep their tickets and rollover the excess into 2021.
Likewise, many people purchased season tickets because they wanted to be there the first season in the new ballpark. If you allow refunds, and come August or so we are allowed to have fans in the stands and there's a "2020 Opening Day", then suddenly a bit of the shine comes off of that 2021 Opening Day and you're going to have some people decide not to invest in 2021 the money they were willing to invest in 2020. A lot more people if Texas doesn't perform well in the shortened-season.
Since all of this revolves around Opening Day, they should simply split it off from the 2020 season right now and offer the following:
1) Willing to rollover March/April/May into 2021 credits, keep access to 2020 "new" OD - 10% bonus.
2) 100% Refund of March/April/May, no access to "new" OD
If you choose Option 2, you get your money back and if there's games in June/July/August/Sept then you have your remaining season tickets, but that first game back (new OD) is no longer part of your package and you will have to purchase separately.