TL;DR - I like shopping secondhand for better quality items that usually align with my personal values better (colour & modesty values, for example) + sizing. But it's heavily location dependent - I have very different strategies in the UK/ HK/ PK!
I would gladly pick things up for pennies at the charity shops* in my tiny British hometown, because the quality of donations were fairly good (I tried again when I went home this summer &, whilst I did still find a some gems, much is also now fast fashion).
I wouldn't mind travelling a little bit to the wealthier suburbs/ neighbourhoods when ai was in school/ university because I could find even better quality items (some even designer!) for slightly more money. Those were still charity shops*, though.
Whereas now, I don't really thrift in-person much anymore in HK - whilst I have indeed picked up some great items, a lot of it is either much smaller than my size (local demographics) or a completely different style sold for much more money than I'm personally comfortable with (the 'normcore' & 90s fashions are popular here, so I've seen 'vintage boutiques'* sell things like baggy Fila t-shirts & Champion tube socks (yes, those white ribbed ones) for £30 a pop - not new!)
So whilst I'm not against thrifting, I'll admit to mostly buying my vintage & secondhand clothing from Etsy these days. Just scored a collarless Dior blouse that way, in a very similar silk to a Dior pussybow I already thrifted from a local HK seller
As for the transportation issue, everyone has their own limits - I see it as I'd rather pay to ship something I know I'll use, rather than buying cheap market tat (just because it's local) that will probably have to be donated after a few wears. Sure, some people might say you can travel further out to go shopping instead for better clothing, but isn't that spending (public) transport fuel too?
Just like some people are ok with dropping money & chemicals on regular salon visits VS others who box dye their hair VS me (only natural, handmade henna), I don't think it's fair to shame folk for making different decisions.
*The term 'thrifting' I've noticed can mean very different things to different folk - in the UK, charity shops exist on the high street (alongside other 'normal' clothes shops). I never shopped more 'curated' shops there, so can't compare those experiences - they're sort of like the Goodwills in the USA, but MUCH smaller.
I also miss 'car boot sales' in the UK - most similar to what Americans call a 'yard sale', but actually everyone drives to an empty field (usually a football/ rugby pitch) and literally sells stuff out of their boot (trunk)! You need to get there super early (5/6am) to get the good stuff though - clothes, toys, kitchenware, everything. They usually charge the sellers a small fee but sometimes set up other things for entertaining the kids (like a bouncy castle & food trucks).
I've used Salvation Army in HK, which is similar to the UK concept of charity shops (run by a charity company/ corporation, that does other sorts of fundraising in the area). But HK mostly seems to have those vintage 'boutiques', where local folk have set it up as their business (so I guess it's 'for personal profit'). I haven't asked how they source their clothing, so it's possible they consign too, but I've never bought/ sold consignment.