Underground cable line

I just moved into my new home, I brought my Xfinity services with me. When the guy came out, he said I wouldn’t need that box because it’s going to have to be a different one. So he installed it and the internet isn’t as good here. Then I received an email about an underground cable line. What is this for? Why is this needed here but not at my last few homes? Is this going to fix the issue with our internet going in and out like it’s been doing since we moved in? Are their going to be any issues with the WiFi while this process is being done?