It is true that in the past people wore traditional clothes, whereas, nowadays, people choose to wear more modern and fashionable clothes. In my opinion, this is a change for the worse.
One of the main disadvantages of wearing the same clothes all over the world is changing the characters of people. There are many nations, with them having their own traditions and cultures, which are sometimes not suitable for another nation. Some people, however, are carrying those cultures while wearing the clothes of those foreign countries. They feel like living abroad, and act like a foreigner in their own country by forgetting about their own cultural identity.
Another downside of the trend is the disappearing traditions of a country. Every country has their own national holidays, when people were used to wearing national clothes in them. However, these days people do not even care about them, usually ignoring the national holidays. Take my country Uzbekistan as an example, previous years people wore more traditionally during the holidays, but nowadays people participate in a national holiday by wearing fashionable clothes. Children aged 8+ do not have any information about the traditional clothes of our country.
Lastly, if people do not wear cultural clothes, the national identity of the country may disappear. Some countries are well-known because of their history and traditions. Lots of tourists come to that country to view its culture. By not frequently wearing the traditional clothes of a country, its traditions may not long be lost.
In conclusion, I can understand why people like wearing fashionable clothes, but they should also keep wearing their own cultural clothes for not bringing some problems mentioned above.