Maybe (old) computers... but lousy internet connections! A friend of mine told me that it takes him ~5 minutes for a google search - and this is not the PC being slow...
Until Bitcoin could be adopted there, the Blockchain would be so enormous that they can't even update it in realtime!
Well I dont know about other third world countires but I live in a third world country JAMAICA and actually our IT infrastructure is pretty good as far as I think we have up to 100mbit connections available in all cities and also 95% 3g coverage at (1.5mbps) and 95% 4g coverage at 6mbps (I can drive around and be connected monitoring my miners anywhere I go no problem). I'm pretty sure there are lots of places in the USA that cant get anywhere near those connection speeds.
Right now the average Jamaican is connecting to the internet at 20mbps, so dont knock third world countries