Because bitcoin is also a part of global economy. It's not out of economy that wouldn't affect. It's like when you have pain on your teeth then it will affect on your all body. I have noticed even gold price is dumped as well. It's normal behavior during global recession, some product will dump which isn't compulsory  for our daily life like gold, and some product price would be more higher which compulsory for our daily life like foods. So bitcoin isn't compulsory for our daily life, we can live without btc but we can't alive without foods. So most of people sold btc for real cash and they like to hold some cash for emergency situations. That's how global recession affect on bitcoin.