interesting subject - it doesn't just depend on industrial history, the inland revenue or it's equivalent has a large effect also!
There is, as Old Smokey says, a large movement to cut down the basic salary for all jobs, not just aviation - some smart accountant realised that the basic salary is the basis for many things such as pension, social insurance or other benefits, hence the company can save considerable money in trimming it, and the added bonus is that if you're sick or can't work you will receive sod-all. The sales pitch from the company to you is that the rest of your remuneration is far better related to either the type of work or the amount of work you do, and how well you do it. It's also an artifice designed to save you tax in many countries, given a certain or large amount of your payments outside your basic salary may not attract the same tax levels or be tax-free. There are many of your aviation brethren around the world on a Mickey Mouse basic salary that is considerably boosted by extra tax-free or low-tax payments, and there are many cases around the world where pilots are given lower tax rates or made-up "allowances" specific to them that allow them to pocket more of their wages.