So to answer quickly to your question: there is any technical reason or flaw about AMD cpu, gpu combo?
No there is absolutely not, the fact you see only few laptops with these specs do not correlate with technical means.
8GB vs 4GB: there could be many explanation, could only suppose imo, to lower the laptop cost and/or save space on the motherboard near the gpu and/or depending the resolution.
I think it's simply because ryzen is quite new and second because of laptop manufacturers market shares.
Ryzen platform is quite new so it had to be build from scratch on laptop side.
Laptop manufacturer worked for many years with intel, so that's why you see now the vast majority of them based on intel platforms.
Even on intel side, i found both configurations with 4/8GB of ram, depending the laptop.
So if you look for a AMD cpu/gpu combo go head, as always look for how the laptop is built, it's reviews and if it fit to your needs, as any other laptop in the market.
Sorry for the late reply.
I'm sure I saw Ryzen 7 2700u laptops but now I only see 1700. I'm starting to think that too much processing power and memory is either too hot or too power hungry for a laptop
Yes the 2700U is a quad core 8 thread with a integrated GPU, fully developed to be a portable cpu.
The 1700 is a eighth core cpu with 16 threads based on the desktop cpu.
So obviously it's more power hungry and warmer, it double the numbers of cores but it also double the performances for multithread workloads.
To be honest i did not checked the reviews for you, but rest assured that a ryzen 1700 is not power hungry at all if one take into account the number of cores, especially at lower clocks.
If the laptop is well engineered, i see no issues incorporating a 8 cores ryzen into it, any big laptop manufacturer should be capable to develop it.
Again if you need so much cores into a laptop, you can't expect neither that the machine would run cool, as a basic dual core one find in most all the laptops.
If your need something with so much cpu horse power, leverage the reviews and the users opinions then decide if suit your needs.
Check if the temperature and power consumption are acceptable, but again from a purely technical standpoint, i see no issues at all incorporating a 1700 in a laptop, if it is well developed.