Plaid have been a bit stagnant around here, where I live the representation is almost invisible and why would people vote for a party that can't even promote a representative in the third largest city in Wales? Also for many people they promote 'Welshness' more than promoting Wales, so they tend to put a few people off as they very often don't engage with people and on topics that are more important.
If they got their fingers out a lot more people would support them, including myself.