It's pretty simple:
You can't know if 75% of players left Elite or if the same amount of players spends 75% less time in Elite. Or a combination of both.
PS
Or if just everyone played at the same time due to the release while people usually login at different times.
You problem is - you dimiss the data before even looking at it. We have 7 month prior of stable data, no major iregularities apart from Alpha. Almost same numbers, up and down, up and down each week for months - and this week we are at 50% of those numbers. There are some factors that play small role, cause it's summer. But again, we are talking about gamers here not the regular people, specially younger ones, for whom Summer is just more time playing games at the computer. And Pandemic is still going, some countries still on lockdown, less people are travelling.
But all of this small factors, are compensated because of DLC release - lots and lots of players come back to check it out for a week or two, and then gone. The population increase is massive, and that's what that graph reflects - it's not "people played more in the first few weeks, but less now or at irregular hours " - it's " people came back, didn't liked what they saw, and left ".
There is a graph next to one i posted, that records player numbers every 10 minutes. If players simply switched gameplay time, it would have reflected there. But there is no data exist to back up your claims, other than your own baseless speculations.
