Hi Nima31,
As Karl suggested with his explanation, the reason would be relationship Contact -> Account (Account),
while Contact -> Account (Company Name) is actually what you need.
You could find detailed description of relationship definition in segment via link below:
https://docs.microsoft.com/en-us/dynamics365/marketing/segments-profile#move-between-entities-with-relationships

Contact -> Account (Company Name) will query all contacts by specifying their parent account(Company Name) value,
(account is starting side, Company Name is a lookup field for contact entity, Contact -> Account is N:1)
so your requirement could be met and your doubt could be solved by what doc has described and Karl's explanation.
The one thing that may confuse us would be that why Contact -> Account (Account) relationship exists in OOB drop down list, while I didn't find Account field in account entity.
Regards,
Clofly