> Collecting PII is NOT illegal, as far as I can see. Nor can it be illegal.
Article 6 [0] is phrased negatively, making collecting PII illegal unless x or y. These points cover all the use cases the lawmakers deemed valid; a real-estate agent may collect PII because of 6.1b (taking steps to enter a contract at the request of the data subject). Should a new, possibly valid reason to collect PII come up it would first need to be checked and then added to the list.
Since most websites and online services do not aim to form a contract nor fit points c-f, they have to obtain consent by the data subject (6.1a) to make collecting PII legal.