Don't be so quick to read between the lines that you forget to read the lines!
You seem to be confusing a BBC News article based in large part on tweets with a prime messaging push by the government.
As the article points out, many cycling lanes have been introduced. The infrastructure has been changing, is changing, and will continue to be changed, as both supporters and critics alike attest.
Your original tweet suggested that putting up new signs would have no effect because people drive whatever speed they feel is safe. This is true, which means it's notable that critics point out the average speed in Paris is already below this new lower limit. So either the infrastructure changes have had a positive effect and now it's time for the limit to catch up, or the traffic is bad and it's time for the limit to catch up.
Either way, your pessimism seems to be unsupported by any of the supplied evidence.