The being nimble and touchy relationship stuff is nice, but the real reason you dont need a cofounder is: why split the equity 50/50, 75/25 or whatever it is? You used to need partners to share risk (mainly the infusion of capital). In this industry there are very small barriers to entry, faster returns, and plenty of money available if you have a good idea. Meaning there is very little risk on the part of a entrepreneur.
Why give up a substantial chuck of the equity for a "co-founder" when you can bring that same or similar person aboard 6 months later for a percent or two (5 at most) and get the same results.