Because it is not very crowded. Except weather is amazing, so locals go there to walk. During winter you can even lay down and walk on water. There is path newly made, but still not all over the valley. You can take some tea and snacks and enjoy the sunset. The worst thing about it - no public transport goes there...You need to take taxi or smth.
Feel the nature of Kaunas and its surroundings. It is pure nature piece there. You can take beautiful pictures there, you can calm down there or just enjoy the moment. There is also a place for picknick, so take your foot and enjoy :)
Do not forget, that going by public transport is not very good.