I would guess the reason is that while L1 is not stable it is still easy to maintain with minimal thrust and the instability of the point means that things 'pas

I would guess the reason is that while L1 is not stable it is still easy to maintain with minimal thrust and the instability of the point means that things 'passing through' do not need to work hard to leave the orbit. The unstable Lagrange points are not places that will collect unpowered/unguided objects or debris but they provide easy station-keeping opportunities.