What's stopping you from buying an angle-grinder resistant D lock?

I'm interested in people's thoughts as I'm currently developing my own grind-resistant lock. I appreciate this is not London-specific but thought it'd create some good discussion considering how prevalent bike theft is in this city.

• Is it the perception that they are still not secure enough and if a thief really wants your bike, he'll get it?
• Too expensive? How much would you consider paying for one, in that case? Providing it's of similar quality/security as something like a LiteLok X1 or Hiplok D1000.
• Heavy/clunky/impractical?

I assume in many cases the answer is a combination of all three but it would be interesting to hear everyone's thoughts.

I should clarify that this post is aimed at commuters and casual cyclists. I don't expect people to lock up their S-Works SL8 outside.