A80 might be the expensive A series, but the users of A80 are very less that makes Samsung to neglect the updates. Samsung focuses on the variants on which the users are more.
Example, A50 has the most users and the sales of A50 were at the maximum in A series, which makes it unique from the other A series. So, you can still see A50 under monthly security update list, which even the A80, A70, A70s, A50s or the latest A51 or A71 are also not there in the monthly security patch update list as they fall to quarterly security patch update list from the date of launch itself.
Under samsung policy, priority models are not based on the cost, it'll be based on the sales over that particular product.