That's sort of a subset of the real answer: the in-demand talent that the companies need so much of are usually left of center, and relatedly appreciate some things that are more common/better in left-er areas: public transport, decent public universities, support for biking/walkability, friendliness to cultural/ethnic diversity, friendliness to LGBT people, stronger social safety net.
There are things that liberal areas are worse at, of course: housing costs are usually higher, they're not as accommodating to religion, taxes are higher, some regulations can be stifling. But most techies are less concerned with these latter things than the former.
There are things that liberal areas are worse at, of course: housing costs are usually higher, they're not as accommodating to religion, taxes are higher, some regulations can be stifling. But most techies are less concerned with these latter things than the former.