They were trying to keep the bottom line low. I can pretty much guarantee you I own more games than you and I have not had much of a problem with this. Sony made it very easy to upgrade the HDD in a PS4. An external is just to slow and I would not deal with it, USB 3.0 is only about half as fast as a SATA connection (in reality, on paper it is closer than that)
I dont think thats true.
All of my games are installed on the external HDD (the xbox one makes that your default unless you select otherwise I think) and all load faster now.
In theory, they should be pretty close. But in practice USB 3.0 has been shown to be a good bit slower than SATA III. Not really sure why...maybe there is just extra overhead with USB 3.0? Though I have heard that many USB 3.0 ports don't actually run at full speed.
This is 100% accurate, as I said on paper USB 3.0 is not that much slower but in reality it writes at roughly half the speed as a 5400 RPM HDD on SATA