Developing a new timetable at VIA used to be a process which took several months in which crafting a new cycling plan is by far the most time-consuming task. With the arrival of Covid, the entire lead time shrank to 2-3 weeks (or even a single week in late-March 2020). The only way to make this happen was to drastically reduce the number of iterations which was circulated for feedback from the various stakeholders and that required that all train sets were identical.
By September 2020, enough timetable scenarios had been developed ahead of an actual management decision to increase service, so that HEP cars could be reintroduced (IIRC, the weekend-only trains which were reintroduced on September 11, 2020 were all-HEP) and I believe that they remained in service since then…