It's a good question, but just about all of the indications we have are thankfully that it's a combo of bad luck and bad defense:
- Except for '23 his peripherals are consistently stellar. This should generally be your north star. There are a small number of exceptions but when in doubt chase guys who do well in terms of strikeouts, walks, and homeruns
- And unlike say Ben Brown it's not a situation where "yeah he struck out a ton of dudes but the guys who put it in play all smoked the ball". Cease has pretty normal hard hit and barrel rates. His Statcast xERA this year was 3.46, a run less than his actual ERA and ranking right in between Joe Ryan and Freddy Peralta
- Cease has had a lot of bad defense behind him for his career, including this past year. The Padres as a whole ranked 20th, and Statcast estimates that Padres' fielders cost him specifically 5 runs. That's about a third of a run of ERA
- That means the other two thirds of a run is sequencing. Luckily this appears to be noise. His peripherals are nearly identical with runners on vs bases empty (3.57 xFIP vs. 3.54). He got hit harder with runners on, but I have a hard time justifying him magically being more hittable without that showing up in degraded strikeout, groundball, or homerun rates
There's some gray area when a guy's ERA doesn't match his peripherals, but all the usual suspects for cases where it turned out legit come up empty here.