Why still the old fashioned way...?
Because simply put, multi-cyclone tech has only just started with other brands and thus the brands won't want buyers to be detracted from the current older style filters. For Hoover UK, it was far longer - 2008 for their Slalom and Freedom uprights with the "Airvolution" take on multi-cyclones. Other brands have been slower to take on this design since their models still use the older design. Vax were one of the first in the UK outwith Dyson to offer multicyclones in their "Zero" range, but not many buyers know this, well before the Mach series was introduced.
Other budget brands are still relying on the paper pleated cones because they don't offer multi-cyclone tech yet - and the new design isn't as cheap as you'd think - otherwise they'd be mains power hand vacuums offering multi-cyclones by now, as well as the latest ranges of stick vacs or what have you, other than the Vax/Hoover Linx that has been out for years beforehand (but at an expensive cost price in the UK).
As much as I admire your scientific post, Steve - the multicyclones really haven't improved anything - end of the day you still have a filter to wash out once it gets clogged. It just means it doesn't shorten out as much or doesn't require as much cleaning as paper cones do.