For most it's a feeling of bad-assness. But for others it's a feel of nostalgia that the CB750 yet again stands up and says.... "I have that"
And for others, it's a feeling of
"my starter stopped working and I never bothered to fix it because it kick-starts so easily, and the battery lasts longer, and I'm too lazy to fix the starter but not too lazy to kick-start the bike every time and now I'm contradicting myself and this is all too confusing, plus I think I look cool kicking it!"

Not to mention the fact that not having the option of electric start really forces you to get to know your bike on a more "intimate" level. Depending on what the temperature is and when the bike was last ridden, you really have to know exactly how much throttle to open, and how much choke to use to get the bike to start without wearing out your leg.
It's also an added anti-theft device, without actually adding anything to the bike.