Earlier quoted context omitted.
Because “shares” are not all the same. Preferred vs common, so unless you negotiated some kind of preferred share terms, assume your shares are worthless. For a non publicly listed company. For a publicly listed company, the details are all publicly available, so the different types of shares will have their different prices be easily available to see.
If that's true, when a startup is making you an offer for ISOs of common shares, and explaining it... how likely are they to know that, in event of a successful exit for the startup, your shares would be diluted and preferenced to 0 value? (The two most recent offer equity components I accepted were "2%" and "a million shares". On the latter, an upper exec did a kind of deal-closer meeting for their offer, showing me…
If they have any experience, or even just browse a forum like this, they should be 100% likely to know. The person on the opposite side of the negotiating table has a goal of giving you as little as possible in exchange for your work (and vice versa).