Because the move itself is not broken or uncompetitive, it is our obligation to preserve Baton Pass for the many Pokemon that make competitive use of it. What do we really lose by continuing to do these specific complex bans anyway? So what if you are clairvoyant enough to discern that one day Baton Pass will somehow be broken in some form again? Are we wasting too much time making these PR threads for your liking? To make the jump from "some forms of Baton Pass are broken" to "too many forms of Baton Pass are broken, let's cut our losses and ban the move as a whole" is not only unreasonable but completely unnecessary. Also, it doesn't help that the only two examples you could think to produce along with Speed Boost pass, CelePass and Amnesia + Iron Defense Mew, are embarrassingly far from being broken. At its core, the move is not broken, so why not nerf it into infinity if we have to? Again, this consensus was already reached in the Leppa Berry thread; try actually reading that thread and the real reason why Leppa Berry isn't banned and I'm sure you'll understand why trying to ban Baton Pass is out of line with tiering policy (except that this is even worse because BP is much more relevant than Leppa Berry!).
In short, 1) the idea that Baton Pass is broken is flawed, because an element that is only broken when combined with other particular elements is not inherently broken and 2) there is simply no reason not to continue with these complex bans; you say that we should "be consistent and avoid complex bans as much as possible", but you have imagined any inconsistencies, because complex bans on moves/items and complex bans on Pokemon are to be and always have been treated completely differently.
Those two examples sound nice, before you realise that hey, there are broken forms of baton pass right now, in the form of ChickenPass in NU and potentially NinjaskPass there too. And as for examples of BP being broken, the full bp chains, geopass, smashpass, quiverpass, gliscorpass and IDScolipass have all been broken. Yes they all have speed involved in them, but the simplest solution is simply banning the move. The reason we shouldn't preserve Baton Pass is the same reason we shouldn't preserve pokemon like Lando-I by just banning Sheer Force on it, we aim for the simplest solution as often as we can, and by nerfing Baton Pass we are going against our own Policy to keep tiering decisions simple.
You say it deprives 88 pokemon of a move (87 if you dont count Blaziken), but of the ones that have Baton Pass slashed on their dex analysis, it removes the move from... 13. Including Combusken and Ninjask, which are potentially broken in NU because of Baton Pass. And that's including cases like Mr Mime and Jolteon where baton pass is not a necessity at all, and such metagame wonders as Illumise and Torchic.
And outright banning BP should have been the decision before. Nerfing it was not something we had to do, and just muddies the water in situations like DynamicPunch in PU. We should just correct the mistake of trying to restrict the broken thing and just outright ban it.