I have no idea why they are publishing pieces like this, and it’s objectively false. Mastodon had over 60,000 sign-ups in the last week, and my feed is as busy as it ever was. It went from like 4 million when I signed up less than a year ago to over twelve million now.
This may be overly cynical, but the same company owns Reddit and Ars Technica.
Articles which would make one tend to expect failure of the Reddit migration are aligned with the interests of that company. This may not be related, but it's hard not to notice.