Well, for example: if the goal is increasing a supply of affordable housing, and the housing stock in question is apartments aimed at at wealthy tourists, does insisting on long-term rentals accomplish this goal? Are Parisians searching for affordable housing really in the market for
these places? Certainly not. So to achieve the stated goal, something else would have to happen. Forced subdivision? Rent control? Eminent domain? Even in France, forcing owners to disgorge property in order to repurpose it for affordable housing seems unlikely.
Now, if there's a big stock of rental places that would otherwise be highly affordable housing, the move makes more sense. But I suspect that while such places might exist, they're rather outnumbered by the other kind of apartment. An Eiffel Tower view doesn't magically become affordable housing unless one removes the windows.
Also, as Rahsaan suggests, this would impact the economy. I have no idea how much, but he might. A tourist spending a month in an apartment is spending money at a retail level that she is not spending if she's in a hotel for four nights, in which case it's going to hotels and restaurants only. That might not matter in a neighborhood where tourists don't go. I suspect markets in, say, the 7th might feel differently.
As with most such moves of this type, I suspect that the hand of the government's interest in affordable housing is somewhat less involved than the hand of the hoteliers' lobby.
Having read some more about this, however, it seems that the initial report might have been a bit overstated.