If people come in through Google because they are searching for something and instead of arriving at the content that was advertised in search results, see a content covering popup, that's not really informed decision making. I think Google has legitimate right to rank sites that do this lower.
If users heard there were better results elsewhere though, they would switch from Google. However, it is more likely that by doing this Google prevents itself from being taken over by a competitor that creates this feature.
If people come in through Google because they are searching for something and instead of arriving at the content that was advertised in search results, see a content covering popup, that's not really informed decision making. I think Google has legitimate right to rank sites that do this lower.