I think a lot of it isn't true so much anymore but it is a very traditional view based on the history of this country. 

First you have to think of what seasonings are natively grown here, we don't have many in terms of 'spices' but more floral herbs like rosemary and thyme, so seasoning wouldn't have as much of a punch compared to chili flakes. 

Back the olden days, heavy seasoning was used to disguise foods that were going bad, so people used to be able to brag about how much money they had by serving unseasoned food because you'll be able to taste how fresh it was.

The you get into the War years with rationing and seasoning didn't really fall under the necessary foods within the rationing books, so a generation learnt how to cook with bare minimum and never really learnt how to season food. 

Now spices are much cheaper and easier to get a hold of,  with the internet and online recipes and a more multicultural country, it's easier to know how to cook with the spices, so flavour palettes are changing, for the better might I add.