Here's a stark new reminder that investors don't really care about Yahoo's core internet business

Despite generating roughly $5 billion in annual revenue and drawing 1 billion monthly users, Yahoo's core internet business is valued at less than zero by the public market.

Instead, most of its value is ascribed to its ownership stakes in Alibaba and Yahoo Japan, which together outstrip the value of Yahoo's $35 billion market cap.

And on Wednesday, investors showed once again that Yahoo's stock value is almost entirely tied to Alibaba's performance, not Yahoo's core internet business.

Yahoo's stock is down 4% Wednesday afternoon after Alibaba disclosed that it's being investigated by the SEC for its accounting practices. Alibaba shares are also down roughly 6%.

The news comes against the backdrop of AT&T joining the bidding war for Yahoo's core internet business on Wednesday. Yahoo's currently running an auction for its core business, which includes its search and mail properties, and theoretically, having a big player like AT&T join the bid should be good news since it sparks more competition over the price.

But Yahoo's stock doesn't seem to reflect any of that, as it continues to slide alongside Alibaba's stock.

It's a stark reminder that Yahoo's Alibaba stake is its most important asset, and investors most care about how to monetize it.

Here's a chart that shows the stock movement of Yahoo and Alibaba since 2014: