Filling the local map is part of the fun for me as there's finally a small perception (or call it illusion if you want) of something rewarding, something that I've 'worked out'. It could be so much more agreed, but this aspect already
is so much more than the cheap giveaway from the ADS. Getting any ADS functionality back into the system would seriously spoil this effect for me. On a scale of 0 to 100 the ADS would be the 0 while a perfect system would be on 100. The FSS is somewhere around 50 to me while putting the ADS back would spoil any perception of an achievement to me.
I don't claim the FSS is in any way perfect or (sadly) challenging but that pretty much is the point, the answer to your question and why the FSS is so much more popular than the ADS. It is a little 'something' and clearly better than nothing. I just wholeheartedly hope that it'll never get diluted by the ADS to mollify a handful explorers with their very special exploration habits.
I'm all in for taking it even further towards the 100, but I'm afraid that's going in the polar opposite direction of what you want to go back to. So I accept the current state as the happy medium that I can barely accept with clenched teeth, whereas what you have in mind is like mixing up hot and cold water. Doesn't work for me, totally unacceptable. For
you it would perfectly work of course as
you would lose nothing, while all those who never liked the ADS just had to suffer over the last 5 years. Something I'm pretty sure you never cared about.

Hope this answers your question?
Please keep in mind that's only one reason why both can't co-exist. It's my very personal reason that matters the most to me. I've already seen less subjective reasons that are also constantly ignored as well, so what the heck...