Why aren't more Welsh people nationalists?

There's no easy answer but two things spring to mind, firstly the Act of Union was in 1536, and passed off relatively easily because of the Tudors' Welsh heritage. This was way before most of the institutions we take for granted were developed, so Wales was assimilated right from the early days of modern history.
Secondly, Wales embraced international socialism, Keir Hardie was the first Labout MP, voted in in Merthyr. This is the opposite of nationalism. Most Labour people despised Plaid Cymru until relatively recently.
There was a massive influx of immigrants, from just about everywhere, into the valleys of South Wales in the 19th century. The population of Merthyr shot up from a few hundred to 100,000 because of the iron and coal industries. There was very little Welsh spoken there until the Welsh language movement really got going in the 1980s.
Also, we have a lovely self-deprecating sense of humour, we know we have the best beaches, the loveliest people, and bugger the rest of you.

Welsh nationalists just keep quiet and are dignified
they have no need for constantly trying to assert who
they are the "mongrels" are obsessed with NO identity
NO culture NO indigenous language NO race and NO
political party in British parliament NOBODY is "english"
they are all bits of people from everywhere else (DNA)

The IRISH WELSH and SCOTS are all cultures in their own
right and are closely related to one another England are NOT
apart from old very small regions of Cornwall and Northumbria

England are the odd ones out the misfits the non race non culture
and of course they are the most obnoxious and the most arrogant

Most Labour people despised Plaid Cymru until relatively recently.
There was a massive influx of immigrants, from just about everywhere, into the valleys of South Wales in the 19th century. The population of Merthyr shot up from a few hundred to 100,000 because of the iron and coal industries. There was very little Welsh spoken there until the Welsh language movement really got going in the 1980s

In the last census,more than half the population didn't call themselves 'Welsh'.
Too many incomers are living here.

Less of a class divide between England and Wales.

It is impossible to stop the Welsh from being proud of being welsh. They are very sharp too... why pay for additional layers of government and have more people lording it over them when the present ones aren't even delivering properly?

They agreed to but backed out at the last minute .

The Welsh are not stupid. They remember they come from an economy that was almost entirely dependent on coal and steel production and they don't want to go back to that competing with low world prices.

The Welsh are more sensible and know their place , the others you mention are stupid enough to think they have any relevance in the world..... they don't.

Culturally wales, england and scotland are pretty much the same, there is no assimilation now, it's already happened, it's all just trivial crap now, the scots had their vote and wouldn't f#ck off, kinda like when an angry teenager threatens his parents he's "leaving home" for attention, and then returns an hour later when he gets hungry

Northern ireland is a different story altogether