There are a lot of trade offs in battery sizing for these cars. Larger batteries mean more cost and weight, which impacts efficiency.
Multiple studies have concluded that there isn't enough of the battery raw materials and mining infrastructure to convert all of society's driving to EV only, even for relatively small markets like the UK by itself. The biggest environmental bang for the buck of scarce resource is to go hybrid or PHEV.
The Clarity's battery allows me to eliminate 95% of what I did consume in gas. Getting rid of that last 5% would require something like the Leaf Plus with the 60kwh battery or a Tesla. Tripling the battery size or more to eliminate that last 5% is far from efficient use of those resources.
For each driver, the battery size sweet spot will differ. If my regular commute was within range of some of the shorter range PHEVs, those could have been a good option for me. In my case, going with a lower battery size would have really boosted the gas consumption. But going larger only nibbles at that last 5%. If my commute was a bit worse, then an even larger battery would have been very tempting.
I do admit that the idea of going all EV is tempting. That drove my decision to go with the 2013 Leaf as my first venture into EV driving. That had eliminated all of my commute gas, but then my job changed and I now have a much longer commute. With the Clarity, I think Honda has hit an excellent balance point.