Because it acquires an asset worth roughly that much, it’s neutral. GME is (probably!) not doing a huge at-the-market offering, they’re creating the shares and immediately giving them to eBay shareholders.

In practice the price paid for the company being acquired is usually a bit higher than the market value (so the shareholders take the deal), and the market usually punishes the acquirer a bit and the resulting entity’s stock will fall a bit. (This is most definitely not investing advice.)