Pilot costs do have an impact on the cost of the operation.
Last full financial year fuel costs were about 1/3 of total costs. So say the B787 is flying a 16hour sector, with 4 crew. Average burn (Very rough figures here) 5 tonne/hour costing $5000 per hour, for a total cost of $15,000 per hour. (Any lower cost for fuel will mean crew costs have an even higher percentage impact on the cost of the operation).
Flight crew cost $300 + $200 + 2*$100 = $700 per hour, but costs of employment (super, allowances leave, regulatory compliance etc) probably increase that at least by 1/3, so call it roughly $1000 per hour. That is 6.7% of the total cost of the operation, just for pilots.
Now imagine you have to pay double time (or more) for every hour beyond 14 hours, and 33% night credits etc. You would then be looking at pilot costs around 15% of total costs for the hours when overtime is paid.
When airline margins are historically very thin (1.6% last year according to IATA), this added costs erases the profiitability of the route. Therefore, we cannot justify the route, and therefore we miss out on the associated expansion.
Demanding double overtime and night credits on long four crew routes would kill the profitability of those routes, meaning we don't do them, meaning we have less growth, meaning we all lose out on increased income and promotions in the long run.