We can of course keep our eyes open, but I was speaking from JA's position, whose eyes were perhaps not that open, because of the times she was in, just as we cannot see things which people 200 years from now will see.

In fact we see a lot but are unable to do a thing about it, and continue to do it.
Cars pollute, and continue to be used. There is a long list of examples.

I see JA in a similar situation.

Another point is that;
The fact that in 'Emma' servants have been mentioned so often in the day to day life, I feel it was not deliberate on JA's part to not mention them in other books.
I think perhaps JA thought they were not necessary or were not required for the essence of the story.

In 'Emma' it was necessary to mention servants. They coloured the life in a small English village, which was what JA was painting.

In Persuasion, it is about Anne, emotions, suffering etc.

Just my 2 cents :-)