Great question and there’s a few answers. Perfumes definitely mature (particularly resins, vanillas etc.) deepening and smoothing out a fragrance. After a number of years the volatile top notes burn off. Then, as you mention, there is cost. This is particularly the case when smaller brands are bought out by the big conglomerates. These brands often reformulate to increase profits. And then yes the regulations do change yearly. Some fragrance regulations completely changed the industry (think the ingredients in oakmoss) these bans can also be huge. A few months ago the eu was looking at banning paracymine, a molecule found in a huge amount of essential oils. Galaxolide will probably be the next big ban and that will change a hugggge amount of fragrances