I'm talking Apple specific here but the number of iPhones openly advertised on eBay as "bad IMEI" is beyond a joke. That fact alone and that eBay does nothing to curb this practice tells you something right there. Combine that with the fact that these "bad IMEI" phones still command a very high price, almost as high as a "clean" phone shows that the market in stolen phones is still very much alive.
Despite Apples' best efforts at implementing this kill switch, the second hand iPhone market has now become a gamble, because what you see is just the tip of the ice berg. Leaving aside the more "honest" sellers that openly advertise the phone as "bad IMEI", you have to consider the remaining sellers that son't explisitly state that. You buy a second hand iPhone and it may have a bad IMEI or be iCloud locked to the previous legal owner and you have no way of knowing that in advance.
When Android and MS implement kill switches this current iPhone situation will only just expand to the other platforms. I don't see a reduction in thefts as long as stolen phones still command a hefty resale price, kill switch or not.