they are still in crypto. they just diverged out into other cryptocoins while still within the common framework of crypto-economy
I don't think that they entered in altcoin communities. At least not all of them. Those which were here since Bitcoin or even the apparition of Bitcoin don't have any reason for changing their focus on other coins. Maybe the reason for which these libertarians became more or less silent is the fact that their voice is covered by all those which entered in crypto hoping only to get rich over night. Maybe libertarians which believed in Bitcoin and in its power to eliminate middle men feel disgusted by seeing so many people around them talking about crypto while having only greed in mind...
that is a considerable factor. the sub 100,000 OG bitcoin libertarians of say 2013 are washed out by the 100m capitalist consumers
most notable threads are actually when there is disagreement of "bitcoin roadmap" that many do fork/ico genesis off to other networks.. due to fighting the moderated hierarchy of capitalist devs who have the merge decision power
(note majority core devs with merge capability are corporate paid now) and most "voluntary devs" who have merge privilege only have their merge privilege on other projects
its also said that alot of the the capitalist consumers fork/ico genesis off too(hence the useless greed pump dump coins of many thousands of crap coins)
sidenote
2009-2014 was an era where bitcoin was seen as "true money" the collective self governing worked(consensus). people had "keys" and "signatures" that were proof of ownership.. in reality and in legal jargon of property law protected rights
now we have corporate hierarchy of paid and moderator protected reference client CORE(central) development. and when it comes to coin ownership.. in legal terminology , we have "witnesses" and "scripts" and "seeds" which has changed bitcoin from a property ownership law system of value ownership. into a capitalist legal jargon of not so protected property right of value
alot has changed in a decade, and some have noticed, and the same some have noticed those who are siding with the new regime