To be honest, for the average person who probably already carries and uses only one or two payment cards, Curve does not add much value. Most likely, it just adds unnecessary complexity for most people. The cashback is too insignificant to be worth the hassle.
However, some of us, for whatever reason, have many financial accounts, maybe across multiple countries (both EEA and non-EEA) and for us Curve actually simplifies things.
For example, I have income in USD and CAD going into US and Canadian accounts. Curve allows me to spend that money where an EEA card and/or billing address is required and still charge those non-EEA accounts directly (and even do FX at 0% markup if needed).
Also, I like to track my expenses and being able to generate a single CSV export of all my transactions across all my cards saves me a lot of time.
Some other minor benefits are the ability to use Apple Pay for normally unsupported cards, and to use chip+pin and/or contactless for US chip+signature / non-contactless cards.