several reasons
see my above reply - compared to cockroaches they are a higher form of life and so by Aryan-racial standards are worthy of preservation (heh heh heh - hope you liked that ;)
secondly I wasn't aware of their bite, they seem so nervous and scared of people that I'm not too worried there - but I will be from now on,
lastly, I don't like 'splat', I prefer the more hygenic 'whoosh' of vacuuming, followed by a good Baygonning into the vacuum cleaner