There are no "tricks" here. There's just supply and demand. The yield management people and/or algorithm are offering fare buckets that maximize the revenue for the flight.
On a San Francisco to Las Vegas flight, which is largely a leisure route, the pricing suggests that fare flexibility is worth more than a bigger seat for an hour. That makes a lot of sense to me.
What would be irrational is if the refundable first fare were cheaper than any of the main cabin fares. I bet that never happens.
In conclusion, per the OP,
Normally I would consider LAS-SFO to be too short for first class, but I'm considering it
The algorithm appears to be working. ;-)