EasyJet along with other LCC have been charging for bags for years and are a set price and are not calculated in relation to the sector distance of each flight.
Have you not looked at the EasyJet website to see their baggage charges!
This is why the likes of British Airways usually come out cheaper once that you consider baggage charge and allocated seat charges.
I fly with British Airways and you get one 23kg checked in bag and free seat allocation within 24 hours of departure although being a British Airways Executive Club member my preferred seats are always allocated for me even though I have the option at no added cost to change them.
Do a few like for like flight comparisons and the difference in price between BA and EZY flying from LGW and the price differential between them isn't that much most of the time plus you earn miles on your BA flight adding towards even more flights with the airline.