Worth here is most likely return on investment. If it costs $4.5bn to purchase the patents but they are only license-able for total of $1bn, or there's a chance someone could get them invalidated, or your violation targets figures out a way around them, you could have ended up spending $4.5bn for a lemon. Spending $4.5bn on an investment that doesn't at least break even doesn't look good to shareholders.

Something is only worth what someone is willing to pay if there is a market. There's a only a market when a buyer and seller meet. If someone is acquiring the patents not to (re)sell them, but to use them in an offensive or defensive mode, there is no market to consider what people will pay for them.