Because 1) you don't expect this to happen (confidentiality) 2) you're still setting up your company/idea which requires other administrative tasks which require time.
They want you to impulsively buy a domain out of fear of it getting hijacked.
I still don't see why not, it takes a few clicks and costs a few dollars. It seems that if you are a person that expects this to happen then it's a good strategy.
Otherwise you just decide which domain search you trust and hope your domain remains available.
Because 1) you don't expect this to happen (confidentiality) 2) you're still setting up your company/idea which requires other administrative tasks which require time.
They want you to impulsively buy a domain out of fear of it getting hijacked.