I'm guessing that the bike thieves in this area are well aware of the value of this threshold and operate accordingly.
It feels like I'm living in a Discworld novel where petty crime is "designed in" to society. There's a mutual unwritten agreement that the thieves can do what they like, as long as they stick to lower-value items. If you're too poor to afford a replacement, tough luck. Even my home contents insurance was pointless, as the excess was greater than the bike's value.
Obviously this will vary hugely by region and police force. Some of them probably would be happy having easy cases handed to them on a plate.
* Very anecdotally! I don't have any stats on this, and the anecdotes come from a fellow biker who is part of an anti motorbike theft campaign group, so take with the appropriate number of grains of salt.
It's a frustrating problem.
My current commuter bike that I got after having one stolen is a beater, and the lock that's on it cost me more than the bike. Sure, it's not the greatest to ride, but I can leave it locked to the closest lamp post next to wherever I need to go, and not worry a single bit.
Also, I like to think that the big, shiny registration sticker helps persuade would be thieves not to bother. Where I live, bike registration costs just couple EUR, but judging from the absence of stickers in bike racks, hardly anyone does it.