The thing is that LA‘s newest A320s as well as all A321s, which are deployed on domestic or shorter haul international flights, do not even have the possibility of a Y+ cabin, but have a (basically non-changeable) Y-only configuration.

For some reason (maintenance?), there is no aircraft with a Y+ cabin available for the day of your flight or may be they only had a few reservations for up-front, but an overbooking situation in the back, and it was more convenient (economical) for LA to pay compensation to the few Y+ passengers, but to be able to accommodate all flyers. For sure, you could think of more possible explanations.

As a standard, LA NEVER adjusts the size of the Y+ cabin, even if technically that would be doable. Thus, Y+ seats a maximum of 12 on all routes and, even with the usual elite upgrades, there is often a couple of seats free on the flights that I commonly take (SCL to LIM, GRU, EZE or LIM to BOG, UIO or vice versa), hence the actual need for a larger Y+ cabin does not seem to be there or other factors (such as quicker turnarounds) are more important to LA.

I am quite curious to see, what the future holds for Y+ with LA. Will they introduce a proper cabin at some point (as JJ used to have on their single-aisles)? I kind of doubt it given the current LCC-like moves.

Anyway, I quite like the product. Yeah, the seats are the same, and pitch and width only a little more generous, but privacy and service wise Y+ with LA is a far cry from regular Y.