The wave of unionization refers to new unions being formed, more workplaces unionizing, and a general zeitgeist favoring union. It does not refer to total number of union members.
Since the 1980s the trend has been that unions, unionized workplaces, and union memberships have all been on a steep decline (along with pay, worker rights, etc.). It is not surprising that union memberships will continue to decline given the previous trend, but also the confounding variables of union member being more likely to be close to retirement age, rate of unemployment, gig workers, contractors, etc.
However, this trend is starting to reverse. There have been several high profile workplaces unionizing, several high profile unionizing efforts, and a general positive reaction among the working public. Notable also—and very much a part of this wave—are several high profile strikes, near strikes and other direct action. UPS narrowly avoided a strike, UAW are striking, screenwrites had one of their longest strikes, actors are in one of their longest strikes. Amazon has seen walkouts, etc.
This is very much a wave, even though one particular line does not reflect it.
