DO is a completely different service. It's Apples to Oranges. You don't go with GC or AWS just for a bare-bones VM, you use them if you already use (or want to use) their greater portfolio of services.
If you are just using EC2 or GC for VM hosting, you are doing it wrong and are throwing away a lot of money.
Sure it's cheaper, but DO doesn't provide consistent performance or security. Look at their past security problems with users able to read others disks or performance benchmarks for proof.
Amazing how competition works.