Not sure common sense is a factor.
These days you can buy so many classes and types of ticket with limitless restrictions and conditions. If you buy a dirt cheap £40 ticket then it will obviously be far more restricted than one which would cost £160 for the same flight. If you need to be flexible then you pay for a flexible fare, it's not hard. People who don't need to be flexible, like myself, are prepared to sit around airports for hours on end waiting for their departure time. I'm glad of these cheap tickets even if it means I can't jump on any flight I like. In days gone by they offered one fare which was much higher than today's average. I'm not sure why people think they should automatically be entitled to switch to an earlier flight if the ticket they bought and paid for doesn't allow it!
I have used the easyJet facility to jump on an earlier flight a few times, but then they offer (or offered, I'm not sure if it's still around) that on all tickets which the route allows. They also had a policy of flying you back to any London airport if your flight was delayed and another flight to a London airport had space, although again, not sure if that still exists and on which routes that would apply these days.