Can someone explain why SV tech workers are more left-wing to me as an outsider? I always thought these tech workers were more libertarian.
Right-libertarianism was an attempt to unite the libertarian parts of the left with socially liberal elements on the right against authoritarian ideologies; their main distinction are views on property rights and on whether or not de jure vs. de facto rights matter most.
As such it is often hard to place people with libertarian views firmly on a traditional left-right axis. You'll find a variety ranging from the far left seeing private property as illegitimate restrictions on liberty (Dejacque applauded Proudhon's famous "property is theft"), to right wing libertarians who see private property as fundamental to liberty (often invoking e.g. Ayn Rand, Hayek and von Mises), to people in between who want various trade-offs (e.g. mostly protecting property rights but seeing a need for some level of welfare provisions)
My experience is that engineering in general tends to have a lot of socially liberal people, many of whom could probably be described as libertarian, but that the left/right position of their views is often a lot more ambiguous.