You can blame job ads for that. Since nobody wants to be called 'junior' there are job ads that are clearly targeted at fresh-out-of-school people who somehow are also senior developers.

I've seen some amazing young coders that definitely were worthy of that title but they were the exception, not the rule. The tell tale is if the salary that goes with the job is one that you could support a family and a mortgage on. If that's not the case then the position is 'junior'.