I am a collector of flashcarts and I've been waiting for Gateway, Stargate, etc. to all drop in price to add to my collection. There's an experience one can get through flashcarts that they can't get through a CFW and that's something that actually made me interested in them when they were still worth investing in. I don't own any 3DS flashcartat the moment, but that is a factor worth considering.
I know it's shocking to see me "defending" flashcarts but I've never actually hated them, I just hated the teams behind them.
Exactly, some people buy old stamps, some buy baseball cards, people still buy retro games (pay way too much at times IMHO)
I like flashcards because they are essentially a hardware addon/upgrade, gateway is more of a micro SD adapter (accessible via gateway menu or cfw port [github.com/shinyquagsire23/gwcard]) while sky3ds and Stargate are 3ds card emulators, they emulate a legit 3ds cartridge itself, and loading ROMs is done in hardware on the cartridge, this is why you don't need cfw other than for homebrew and region bypass,
Like the dstwo they can include extra ram, cpu or dsp that can work with the 3ds hardware to give it even more capability (it also helps that 3ds cartridge port has a higher speed than nds as this caused issues on nds)
Still 3ds slot 1 has nothing compared the nds days, dserial, Romeo2, dserialedge