If the Buddha praised Samatha, why is it losing importance? It seems like these days, teachers are looking down to Samatha meditation, I would like to understand why, based on the suttas, this the meditation praised by the Buddha.

Could someone explain why Vipassana is so much more present in Theravada tradition, eventhough the Buddha practiced a lot of Samatha? I'm sure there are good reasons.

" And what kind of meditation did the Blessed One praise? Here, brahmin, quite secluded from sensual pleasures, secluded from unwholesome states, a bhikkhu enters upon and abides in the first jhana … With the stilling of applied and sustained thought, he bhikkhu enters upon and abides in the second jhana … With the fading away as well of rapture … he bhikkhu enters upon and abides in the third jhana … With the abandoning of pleasure and pain … he bhikkhu enters upon and abides in the fourth jhana … The Blessed One praised that kind of meditation."

Majjhima Nikaya 108.27
The Pali canon and commentaries do indeed carry considerable encouragement to practice the jhanas. The distinction between samatha and vipassanā aren't really spelled out in the original teachings and it was only much later that the doctrine of the two as separate (and separate-ableon) meditation practices arose. By the time of Buddhaghosa (5th century AD) the distinction was pretty firmly established, though some later teachers dismiss the distinction as unnecessary. Ajahn Chah of the Thai Forest tradition liked to say that samatha and vipassanā are like two ends of a stick - when you pick up the stick, both ends come along See Ajahn Chah's essay on this from his book, "Unshakable Peace".

The emphasis on vipassanā which one finds nowadays came about for very practical and pragmatic reasons, but this topic as a bit much to delve into deeply here. The brief overview is that a method was needed that could be undertaken by a lay meditator on a 30 day retreat and provide the practitioner with a reasonable shot at arriving at the first stage of enlightenment - stream entry. Ven. Mahasi Sayadaw is perhaps the main exponent of this method and it seems to work quite well for many people. In contrast to this, to properly develop "Visuddhimagga-style" jhanas is beyond the reach of most lay people (and most monastics) not least because of the time commitment necessary. 

There's more to the story of course, but that's a thumbnail sketch of the situation.