Earlier quoted context omitted.
Before they were multiple people they were one person. A single person can in fact write a program for a computer.
Sure, some C code, some html, a table here, a colspan there, and you can have a website made by a single person... if we want a website to look like it was made on an 1980s computer by a single person.
If you want to do your own networking, or run email, that's a whole 'nother specialism; but just running a website is easy enough for one person to do.