[graeme]

What makes it fundamentally different from clicking a link?

"Click this link to read more about cinder blocks" "Enter your email here to read more about cinder blocks"

In both cases, there is the promise of more information. Presumably, you would agree that the information in the link might persuade you to buy from the site, assuming you're interested in cinder blocks.

What then would be your reason for being unswayed by similar information in email form?

I'm guessing you just have an opposition in principle to marketing via email, but not an opposition in principle to marketing on a webpage.

The reason email works, by the way, is that you get the user's attention. The first time someone hits your site, they may have 2000" tabs open, they may get a notification on their phone, etc. Email lets you confirm their interest and reach them later. It solves the distraction issue.

[monsieurbanana]

What makes it fundamentally different from clicking a link is that now they will be the ones initiating the contact.

Call me cynic, but I don't think the majority of people have my best interests in mind when they send me advertising emails.

Note the plural in "emails". If you're not interested in what they offer you can't just choose to ignore them, that will only result in more emails.

[graeme]

Well, you can choose not to enter the email and just explore the site. In a non scammy site, you'll find useful information.

The email is an option for those who choose to use it.

Going off your last sentence, you're assuming everyone who sends email is a spammer. Indeed, given your habits, if you have received emails from companies, you've probably mostly received spam.

For instance, you sign to an account or buy something --> company proceeds to send dozens of emails, unsolicited, and ignores the unsubscribe.

This is terrible, but it's not what happens when you enter your email on a non-spammy site. There, they usually send reasonable emails with a working unsubscribe link. Conversions in this case depend upon not annoying the prospect.

If you never enter your email in popup boxes you likely only receive the spammiest of email marketing.

Edit: oops, I thought you were OP, and so assumed you never enter your email. If you do enter your email and get spam - well, I guess we have different experiences. My spam almost exclusively comes from product orders, not from info boxes I chose.