Why did they have soo many different housekeeper women on the show? Wwhy not just have 1 housekeeper for 8 short years?

NBC had only one hit comedy in 1978: Diff'rent Strokes. When they saw Charlotte Rae had become a popular character, they decided to spin her off onto her own show. So Charlotte was spun off onto The Facts of Life.

Nedra Volz then became the second housekeeper on DS, Adelaide. But she was never actually offered a contract with NBC. After a couple of years, she left for another series (which didn't last long), so they needed a third housekeeper, Pearl.

Dixie Carter who played Maggie in seasons 6 & 7 was on Filthy Rich as well as Nedra Volz. They would be on DS together for the Wedding Episodes.

While it’s true that having three housekeepers over eight years felt like a revolving door, each change was driven by a specific mix of business strategy and casting shifts. The "millionaire with a housekeeper" trope was central to the show's fish-out-of-water premise, but keeping the same actress proved difficult for the following reasons:

The Three Housekeepers
Edna Garrett (Charlotte Rae, Seasons 1–2): As you noted, Mrs. Garrett was the breakout star. NBC moved her to The Facts of Life because they desperately needed a hit for their Friday night lineup. Interestingly, her contract had a "fail-safe" clause that would have allowed her to return to Diff'rent Strokes if the spinoff had failed.

Adelaide Brubaker (Nedra Volz, Seasons 2–4): Nedra Volz was brought in to fill the void but was never made a series regular in the opening credits. She was written as "crankier" than Mrs. Garrett to change the dynamic. While she officially left for the short-lived series Filthy Rich in 1982, Volz later claimed in interviews that the younger cast members (Gary Coleman and Todd Bridges) didn't like her and had her replaced.

Pearl Gallagher (Mary Jo Catlett, Seasons 5–8): Pearl became the longest-serving and final housekeeper. Unlike Adelaide, Pearl was made a series regular immediately to provide long-term stability. The writers softened her character compared to the "cranky" Adelaide to recreate the warmth the show had lost after Mrs. Garrett left.

Why the Change Was Jarring
The frequent turnover made it hard for the show to maintain a consistent "mother figure." By the time Pearl arrived in Season 5, the boys were much older, and the role of the housekeeper shifted from a protective "nanny" to more of a comedic foil for Arnold’s antics.

The 1984 wedding episode actually featured a rare moment where all three housekeepers appeared together, which served as a nostalgic nod to how much the household had changed