Because you are doing it wrong ?
You should never buy when there is almost no volume or a bad vibe around a coin.
I never buy low volume coins. I buy coins that have good vibes but as soon as I purchase bad vibes start creeping in. BitBay for example..I thought it was going to do great and everybody was supporting it then out of nowhere they got in some fight and screwed the whole project.
BTC..bought it at 340 thought I was being smart..it fell at 305
CANN. Coin with real use and as soon as I purchased it couldn't stop falling
RDD..bought at 16 satoshi..it fell to 8. Sold it and it reached to 12 satoshi.
XPY..another example. It was pumping normally and as soon as I bought it just so I could get quick 10% profit ..it reached NEW low..it's at all time low right now and that happened after I got in..why couldn't pump go on for few more days.