It's pretty simple really. When thousands of fans say that TLJ killed the franchise for them, of course that's going to affect future entries into the franchise. Even with all the crap surrounding Solo, it should have easily broken even. Instead it flopped. A franchise first.
Given the Blu Ray sales of TLJ (and it will keep selling), especially considering the discontent with TLJ seemed to grow drastically after people saw it, it doesn't seem to reflect what happened to Solo.
And if those people are capable of rational thought, they would know that one movie doesn't necessarily kill a franchise. The writers/directors, etc can. But they are always subject to change.
Solo had a different writer and director. And Episode 9 will be written and directed by JJ Abrams, rather than Rian Johnsson.
I do not like this comparison because it's a story about Han Solo, that to me came off as incredibly uninteresting in trailers.
If something like this happened to the 9th, mainline, Star Wars film, then I'd give credence to that theory. Or if it happened to a Kenobi film, which I know everyone wanted to see. Then I'd think it was very strange that it flopped. For Solo I'm not surprised from my point of view because it's the first Star Wars film I didn't want to see in the cinemas.
I certainly think the discontent with TLJ affected Solo sales, but it was it's concept that caused the major damage, imo. If it was a film about Vader or Obi-Wan, I'm sure it would have done very well. But Disney seem intent on suffocating us with one Star Wars film per year now, so I'm definitely going to be selective of which ones I watch.