The series was very good, but it was still a low budget project. BG1 was developed for an estimated $1.5-3M. BG2 was developed for $7M. I can't even find budgets for Icewind Dale or Planescape: Torment.
But compare that the BG3's $100M budget (closer to $200M after marketing).
These were great games, but they were largely indie games. None of them had AAA budgets back in the 90s. Even at the scale of the era, Ultima XI cost $12M to produce. The OG FF7 cost $45M.