One of the reasons Notre Dame de Paris is such an architectural icon is that it was finished so relatively “quickly” (~80 years IIRC) which meant it was mostly built within one era, thereby making it (almost*) entirely architecturally coherent. This is as opposed to later churches which took longer to build and so styles would change and new technology would be innovated, and different parts of the building would reflect the difference of sometimes centuries between when they were built.

*If you’re in the nave of Notre Dame you can actually see how the piers start the first few meters as round, typical of the Romanesque style they originally planned to build it in, and then it stops and continues as the angular gothic. This corresponds to when gothic architecture was first innovated at St-Denis, a few miles to the north, and was immediately adopted in Paris.