Is a multi-million dollar fine enough to matter?

Let’s assume Apple violated their privacy policy and was fined $999 million, the highest “multi-million dollar” fine they could be assessed. That’s just barely more than 1% of their market cap.

Fines are definitely incentive to do right but the fine must be felt. I’m not aware of any cases where the tech giants have been levied a fine that really hits them hard.

The fine you're proposing would cause a much larger hit to market cap than you're suggesting. Consider, Apple made ~20 billion in profit last quarter, your hypothetical fine would be a precipitous hit to profit margin which, when reported on the quarterly earnings call, would cause an abrupt downturn in share price. Consider the 13% hair cut earlier this year when the market thought Apple was going to miss. Then there's the existential panic of "does this mean Apple is in for more such fines?".

I guess jail time will have to do.

Fines are accounted as overhead.

Watching network traffic is limited to circumstantial evidence, and not even that without a circumstantially isolated environment. Those are a couple of scenarios where these accusations can be made.