It's unlikely we'll see any admission on why exactly the vote was withdrawn, but it's probable that the situation became untenable for the political parties involved, one of which lost massively in the Belgian elections about two weeks ago.
In an short interview in De Tijd [1] with one of the Belgian MEPs pushing this (Hilde Vautmans, OpenVLD, liberal, lost big), and another short line in De Morgen [2] from outgoing Belgian Minister of the Interior who was part of the talks for this new version (Annelies Verlinden, CD&V, Christian democrats), both of them made it appear like they mostly just care about getting it done (because nobody else has succeeded yet). There is a lot of "but think of the children", and zero technical expertise.
This morning, after the press attention, high rank party officials across the spectrum (and from the parties mentioned above) publicly called the proposal dangerous, so it's likely the pressure worked this time.
Next time this can come up for the vote will likely be from Hungary. They are taking over the EU presidency in a few weeks, and have already said this is on the agenda for them. Considering the current political climate there I would assume they are more likely to bring it to a vote, but hopefully that vote is less likely to succeed. Still, there's no time to rest, the proposal isn't dead.
[1] https://www.tijd.be/ondernemen/technologie/fel-privacyprotes...
[2] https://www.demorgen.be/snelnieuws/verlinden-buigt-voor-luid...