The reasons could vary – first on circumstance, and second on the number you are calling. Nowadays, I only promote one telephone number, especially since there is no fax line. However, there could be a chance that someone has one of my home phone numbers.
If you are calling the primary home phone number, that is set to also ring my primary phone. However, if you are not in my contacts, I will likely not answer on my cellular phone. Likewise, if you somehow got my primary cellular phone number – I won’t answer if you are not in my contacts. If you are calling the second home phone number, and I am not home – I obviously won’t answer.
Next, I get a lot of scam/SPAM calls from numbers not in the 412 area code. If I am not waiting for a particular call, and an out of area code number calls me – I am not likely to answer. You do have the option to leave a message, and if legitimate – I will return your call.
Now, assuming you are calling my Google Voice Number, and none of the conditions above applies to you, I won’t answer the phone if I am walking Malak, bathing, eating, nor will I answer between the hours of 10PM and 6AM.