It's the opposite of protectionism. European competitors for these services existed at some point, but because they lacked the advantage of a sufficiently large

It's the opposite of protectionism. European competitors for these services existed at some point, but because they lacked the advantage of a sufficiently large home market and didn't get any extra protection to make up for it, they didn't do as well. Depending on the strength of network effects, they either quickly lost users to the biggest platform, saw the writing on the wall and took an acquisition offer instead, or continue to hold their ground within a particular niche where expanding quickly is difficult (for both foreign and local companies). Any new European internet companies wishing to make it big at home will probably need to concentrate mainly on the US market first in order to have those same network effects work in their favor instead of against them.