The majority of bicycle thefts are not by tweekers as there's a very small used bicycle market. Most bike thefts in England (and most other EU countries) are via organised rings that steal hundreds of bicycles and ship them abroad. What you mention is a very small minority or thefts and quite rare unless you live in a tiny village.

Where I live now bike theft is rampant because it's a port city with a plethora of shipping options to southern Europe and over to Northern Africa.

Also, there are at least 10 bike shops and at least 3 or 4 co-ops selling used bikes for low prices (under £40 for a hardtail MTB with used Deore drivetrains) so no one would buy a used bike from an individual unless it was nice (and then they'd check with the police first.) I should say that's for an island with 200k people.

Also also, tweakers don't have a need to ride a bike as public transport (especially buses) will let them ride for free during non-busy hours. Or co-ops will give them bikes for free as the used bikes are essentially liter at this point, where they used get shipped to Africa as donated bikes (which is how the stolen bikes sneak through not-so-legit African customs.)

The same is true with the used car market (so many that they're essentially worthless.) I see cars for under £500 that would go for easily 5-10 times those prices in the US or GER. Just a market over saturation in England for used bikes and cars.