To go back a few steps as to why a PPL really couldn't do it manually.
1) The pitch power couple of jet engines is immense. Any change in power setting will be too large for a PPL to a)anticipate and b) compensate for, without adequate supervision. Even simple trimming took a long time to get vaguely decent at.
Hell the sim had be frozen an immense number of times (with subsequent repositioning, not possible in real a/c)for my first type rating to even vaguely hand fly it safely.
2) A jet aircraft is an extremely complex bit of kit. Even finding the PTT to yell out mayday would take a lot of head scratching, searching and time. Time you would not have if hand flying it. Many of the a/c i fly are of a different fit (different original customer) and every time i get in my seat i have to spend a little time reminding myself where everything is.
By the time a PPL had found the correct switch (hand flying remember) the a/c would either be in a full stall or in a pretty nasty overspeed and then the mayday would be the last thing ATC ever heard of the a/c
Then deal with all the other bits switches nobs and fiddly bits. You probably would find the right handles for gear and flap, but would you even vaguely be at the correct speed to operate them? I'll even give you +50% and -20% speed but the chances of severely damaging (so they become unusable) a service or stalling is immense.
The PPL pilot would become overloaded. I still become overloaded sometimes and that's why there are 2 pilots.
3) in my company we deal with pilot incapacitation every sim (alternating who is incapacitated). We're taught to yell out mayday and autoland at the nearest suitable airfield. If it's good enough for a commercial pilot....
4) To those who've done it in the sim, remember a significant portion of communication is non verbal. You have a serious advantage of having an instructor (or even just a suitably qualified line pilot) sat just behind you who can point at the appropriate handle, nob etc and who can quickly tell you to nudge on a bit more power etc.
Someone over the radio can't. they'd have to say something along the lines of 'right now press the third button from the right marked with APP. has a little light come on? have you got a G slash S in white in the second box from right just below the green V slash S. okay you now have the approach mode armed just follow the crosses. the sim instructor would say 'press that button' pointing at the APP button
QI (the TV programme with Stephen Fry) found some research from somewhere (not sure where) that found if the A/P was engaged you had a 1 in 10 chance of landing safely. without it you were stuffed.
That's why two pence worth why a PPL could not land a jet aircraft safely.
edited: poster above mentions a lot of the non verbal comms that a sim instructor can provide.