The airline was one of the first low-cost carriers in Europe to take on the model of Southwest Airlines in the USA. This model was based around a single-fleet of Boeing 737 aircraft, and was adopted by other airlines such as Ryanair.
However, the 737 is no longer the only cheap and efficient short-to-medium haul airliner on the market in this seat category. Today, the Airbus A319/20/21 is just as good. In the early 2000s, easyJet started ordering the A319 model in large numbers, and we saw the Boeing 737s being retired.
It remains to be seen whether easyJet will revert in the future to another order for a Boeing product, such as the re-engined 737MAX. Their A319 deliveries have now been completed.
I personally have flown on many of the airline’s 737 flights around Europe and personally thought the livery looked very good on them. It is sad to see them go!