You have to dig a trench or span the wire. Either way you need to clear it with numerous property owners over a vast distance, get approval from dozens of authorities along the way, coordinate work crews, and then do maintenance on the whole thing for decades.
And then you discover that the wire used 50 years ago contained lead and we don't like that anymore, so now you have to pay for massive lawsuits (look up AT&T & Verizon) and rip up all that wire. More coordinating work crews and property owners!
And then they invent a new kind of wire and you have to do it all again.
Launching 1000's of satellites isn't easy but I can see wanting to do that rather than wire up the whole planet.
(in the US) It may be hard for a new company but easy for existing telecom giants. But existing telecom giants don't give a shit about national internet infrastructure quality, so if connecting rural customers simply appears less profitable* than focusing on current operations[1], they won't do it.
[1] Current operations include the obviously profitable "send monthly marketing materials via mail, email, and live salespersons to homes who canceled your services the day they had an alternative," among other idiotic practices.
If it's not hard, why hasn't it happened already?