Supply and demand rules OK; already stated.
If there is the choice of a fully qualified pilot or one requiring training it is obvious who will get picked on that occasion. It is merely from commercial necessity and would be poor business practice to do any other. No-one is entitled to a particular job just because they want it, we live in a capitalist society driven by cost.
In the past I have lost out to pilots with less total experience than myself because I lacked the required type rating. The chief pilot told me that he would have been delighted to have taken me on but the owner of the company said no because it was going to cost unnecessary money to train me.
There is no point whining about it or trying to change the rules to suit one's own circumstances.
However, on the contrary, you may suddenly go up a rung or two on the ladder if you are in the right place at the right time...