Philip Kuhn, whose book Soulstealers (1990) focuses on a widespread panic that took place in Kiangsu province in 1768, at a time when it was believed sorcerers could animate miniature men made out of paper and send them through the air to cut off queues for use in a variety of unsavoury incantations, devotes some time to unpicking contemporary Chinese beliefs about hair.

He points out that the real objection that the Han had to the infamous Manchu ordinance that mandated the wearing of the queue was not to the pigtail itself, but to the tonsure – in the form of compulsory shaving of the forehead – that had to accompany it:

Once the tonsure decree was issued, the conquest regime seems to have focused its attention on the shaved forehead precisely because Chinese loyalists resisted it so fiercely. The reason, apparently, was that the deeper humiliation was not braiding but shaving. Although we lack direct evidence, some castration imagery might have been implied.

Kuhn goes on to point out that, by the time significant Chinese emigration to the US began to take place in the nineteenth century, the decree was about 200 years old, and attitudes towards it had changed as it became normalised:

[Long, elaborately-kept hair], which to Manchu warriors symbolised manliness, to the Chinese symbolised effeminacy [and the tonsure had become] a symbol of restraint triumphant over licence.

In addition to all this, an earlier thread on the same topic led by u/keyilan makes some good practical points – most significantly, perhaps, that a high proportion of Chinese emigrants to the US intended to stay and earn for only a few years before returning home. At this point having a queue would be required once again. So, given the length of time it took to grow hair long enough to braid it, there was also a purely practical reason to retain the hairstyle in the US.

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