Yep, this is the new Sun Country. But it is also the ULCC model. I'd wager that Allegiant would do the same, WOW Air and Norweigan are known for this, also. ULCC's almost never even have the capacity in their reservations systems to book you on another airline, so if anything happens to their flight, which may not be daily, you're screwed with a refund, best case of course.
Sun Country was my favorite airline for many years, I've flown on them a few dozen times to/from MSP over the years and had actually built enough miles for a free roundtrip despite flying only them at a pace of about 1-2x per year usually. I held onto the ticket for a few years, then got an e-mail the other day that I'd have to fly Sun Country in 30 days or lose my miles. OK, better go to MSP. Turns out that in favor of flying SFO-PSP/PDX, SFO-MSP was suspended for the month. OK, I guess I'll use my miles. Welp, Sun Country changed their miles to count for cash, not a full ticket once a target is hit. So now I have about $80 in Sun Country credit(that expires very soon) instead of a free ticket anywhere in the lower 48. Great.
Between the bad press from the Star Tribune and my favorite domestic first class(with cheap upgrades, huge comfy seats, flowing liquor, and ridiculous portions of cholesterol laden Midwest cuisine) going away, I don't think I'll be flying Sun Country much anymore. At least after the cabin retrofits are done. Damn shame, they had a perfect niche and I think this deviation from that model will be the death of Sun Country. They've lost the people of Minneasota, and try as they may to expand, Sun Country will never recover from that. Not to mention that they unveiled a revised livery and started painting planes for 3 years until deciding to paint the planes again to look like Tide Pods. These erratic decisions are probably a bad sign.