The ground. Paris's ground is not strong enough to support high rise building especially in the southern part, where a lot of it have been excavated in the last 500 years (and filled with dead bodies, ie the catacombs). Of course with clever engineering everything is possible, but that really limits the development of such towers.

It is true that the main limitation still is the construction code, which preserves the global proportion of the city.

Because they worsen traffic, as they create high density traffic zones which then need to have bigger highways around it, then you have got the fact that Paris's low city profile is a monument on itself, so city administrators don't want to disturb that too much, then there's the issue of physical construction of em as paris is a river bank city, quite sandy ground iirc

Paris does have areas which have high rise office buildings tho, it is just not the zones people know much about because they are not the touristic areas

a lot of parisians like me find them very ugly and there's already not enough garden and green spaces to out to.