The cause of decline after a reverse split is not the split, it's that the split did nothing to cure the weakness that led to the seeming need for the split. The continuing worsening of the insufficiently addressed weakness is the reason for the continuing fall in stock price.

But when a company returning to health and strength does a reverse split the results can be good, but are mostly not due to the split. I say mostly because an increased price can, other things being equal, increase the appeal of the stock to major investors, or make the stock suitable for inclusion in portfolios and indices.