I'm quite puzzled about this.
When I start my journey, the hard cabin case weighs 4kg alone, the PC + charger 3kg (I have no PC bag), change clothes, EK amenity kit (), legal docs, a bottle of drink, teddy bear, all adds up to 10kg.
On return, that's another story. It's fully packed at around 15kg usually, but never exceeds the size of the cabin case.
So, 14kg is a reasonable limit, but, 7kg is too low.

This said, I'm quite pissed off when I see pax with full loads of stuff in their arms (excluding those with babies).
I know there are various reasons :
> pax who don't want to check baggages, to go faster,
> US pax with the habit of paid checked baggage,
> pax who had to show their purchased goods for VAT refund,
> pax with fragile and ... bulky stuff,
> etc.
But, it is causing trouble to other pax.
I understand airlines cannot enforce strictly the rules, and need to have some flexibility (contrary to LCC), but they should definitively ban abusive pax. Those filling one whole rack for example ...