You don't seem to have much idea what you are talking about.
In an election where over 50% of the electorate did not vote it is entirely possible for the changes in vote share to be brought about by shifts in differential turnout rather than voters transferring their vote from one party to another.
Now some movement from the centre to NUPES probably is happening, but there is plenty of
past evidence that the Ensemble, LFI and RN voters are very different and there is not a great deal of movement between them. Like that tweet posted which claimed that 72% of Ensemble voters chose not to vote rather than vote NUPES/RN, which is backed by the much greater fall in the Ensemble share of the vote in the 2nd round than the 1st.