I don't think you understand the immense amount of data that can be stored on a dual layer DVD. Most dual layer DVDs can hold about 8.5 Gigabytes worth of data.
Now I'm no database expert and I'm not sure how to calculate exact database sizes, but let me give you an example so you can kind of wrap your head around how insignificant adding 15 players for 123 teams would be in terms of disc space.
Each rating and information field would count as one field in the database, and for now we are going to assume that each field fills 100 bytes of data (which is absurd because each two digit rating should take up less than 2 bytes, but we are vastly overestimating here to prove a point). Now if every player has 30+ ratings, equipment fields, name and info, ect. than lets assume that there is about 150 fields per player. So if there are 150 fields x 85 players per team x 123 teams you have 1,568,250 fields of data. Sounds crazy right? Well lets assume that each field takes up 100 bytes, which again is probably way overestimating. What you get is a total of around 150 Megabytes for that database. Not that significant is it? If you use 70 players per team its about 123 megabytes. I'm assuming that each field takes way less than 100 bytes, so the actual database size should be way less than that, I'm just providing an example.
Again I don't claim to be an expert on how databases are stored, so if there is something I'm missing that should cause the database size to explode I'm sure someone will correct me.
I also don't really understand how it could be a memory issue either. Unless they are loading the entire database into memory AT ALL TIMES (which would be stupid) then I don't think its a problem. You think facebook loads their entire userbase with all their data into memory on their servers everytime someone accesses an individual page? Even if the database takes up 150mb, I don't think they are loading all 150mb of that database into memory at all times.
I just think they haven't devoted resources to it because it would not affect their average casual gamer. Simple as that.