Neanderthals: Were they too stupid or just different?

I find puzzling why they didn't evolve more although they existed for perhaps half a million years and they did seem to carry more advanced adaptations to intelligence:

At birth, their brain was of same size as ours, thus avoiding problems with the women's pelvis but, as they grew, their brain would became bigger than ours.

What were they doing with those big brains? It seems intelligence was important to this species but their tools weren't so advanced as the Cro-Magnon and the abstract thought didn't seem so well developed: Their cave paintings and rituals were rare. This doesn't necessary mean they were less smart... Perhaps they decided there was no point in painting graffiti on the walls because they wouldn't catch mammoths more easily. Perhaps they also concluded there was no life after death and that it was nonsense to bury the dead with food and possessions.

So, the way they thought could have been more advanced...

They lived on one of the tougher and colder climates the humans ever lived. This kind of environment would require long term planning and very strong communication and team skills, so the pressure to become smarter would be high. Yet, it was an obscure African human strain that suddenly made the difference, not the Eurasian Neanderthal. A human strain from a warm region where life was relatively easy and the food sources where relatively common.

Why? It doesn't make sense.

What were the Neanderthals doing for half a million years? Why didn't they evolve more?

What if they weren't stupid but just very different, with a totally different scale of values?

Something that allowed them to survive for hundreds of millennia... without the taking the path of the crazy Cro-Magnons, with their technological boom, dangerously out of control.

Therefore, it is important to understand who the Neanderthals were: perhaps they were just stupid primitives - or maybe, just maybe, they weren't stupid at all and that's why they managed to survive for a very very very long period of time, who knows, perhaps longer than the current Cro-Magnon.