Firstly, what do we mean by "politically conservative"?

These labels don't tell the whole story and even less so these days especially in UK politics today.

As you will be aware, many Labour politicians have been accused of being "politically conservative" (The SNP actually call them Red Tories but they can't talk as there are several in their midst too). However, electoral support from both parties even if not the majority of the membership also includes many "conservative" often with a small "c". Otherwise, they would never get into power at all and vice versa. Many Tories have "leftish" views on various issues.

Likewise, folk singers will often feel more strongly on one issue than another. So, it is entirely possibly for "Conservatives" to be sympathetic about many social issues, be anti War, or fox hunting etc and so on.
However, I agree that you don't get that many "right wing songs" and those that there are seem to be frowned upon.

Another thing which hasn't been mentioned is that there seems to be less concern about one's political leanings when it comes to playing tunes. Of course, most folkie musicians also tend to be "to the left" and the bulk of traditional music originated from humble sources although this isn't always the case. The "upper classes", especially in Scotland have had a keen interest in the music too especially during the 19th century and so on.... e.g. Gow and co played for dancing in prestigious ballrooms etc, William Marshall was The Duke of Gordon's butler etc.
There is also a very strong tradition of interest and promotion of piping in the army, police and so on. Hardly left leaning organisations and the clarsach/harp until fairly recently was more associated with the higher social echelons. Nowadays, even I play it.
;-))))))