First question : There is a rule about winning in the first round, you need not only to get more than 50% but also more than (?) 25% of registered voters.
I saw several candidates who got more than 50%, but all are going to the 2nd round, because of less than 50% turnout in most districts.
Just checked : 4 NUPES and one LREM elected in the first round. Historically there are many more.

Second question : The results are very uneven geographically. In the west, the most common second round will be LREM/NUPES. In the north-east and south-east, RN/Republicains is quite common.
Scroll down to the map, highlighting who came first by district.

Ah... I just saw that in the end, the Macronists just edged NUPES nationally : 25,75% against 25,66%

_{It is rightly acknowledged that people of faith have no monopoly of virtue - Queen Elizabeth II}

Adding to eurogreen's:

According to Le Monde, only four candidates were elected at the first round in 2017, but 36 in 2012 and 110 in 2007. Why so? Two things:

Up until the 2010's, the political landscape was essentially the PS and allies (Greens & Communists) on one side and the mainstream right (UMP, now LR) on the other. The Extreme right didn't have that much weight during parliamentary elections and fewer Front National candidates could qualify for the second round, often in a "triangular", with a PS and a UMP candidate. Now, the RN (FN's new name) gets a much greater share of the vote and fewer candidates manage to clear the 50% mark on the first round.

The high abstention is also playing a part: to win in the first round, a candidate must also get a number of votes at least equal to 25% of the registered voters. Yesterday, nine candidates got over 50% of the vote but didn't clear that second threshold: this is the case for Marine Le Pen in the north (53.96%) and Mélenchon's successor, Manuel Bompard in Marseille.

Are the results evenly spread? Actually no, and that is the problem for NUPES whose electorate is mostly concentrated in the big cities and suburban areas. This is why Macron's alliance (Ensemble), whose electorate is more evenly spread throughout the different constituencies, is projected to win more seats (255-295) than NUPES (150-190). Extra mobilization of the left voters may actually reinforce the victory of NUPES candidates in urban areas, but getting more seats than Ensemble looks like a very long shot (another Le Monde explainer if you don't mind a bit of Google translate).