I can't speak for others, but (for me) over the years, this has been an ongoing issue with Spark. I'm on Spark 900/400 ---- It'll be great for a month or so....then for months it'll download off newsgroups at 4Mbps or 7...or 10. And then it will be back at full download speeds. It's like off and on for good download speeds.
I've never been able to figure it out (the old rebooting this or rebooting that) but today Spark (Spark is acting up again) is at 3 MB/s vs my Starlink connection at 30MB/s +