B&L is worth a lot less in an IPO then in a sale.
If sold, the buying company can leverage its own infrastructure as well as elminate jobs at B&L to improve the margins of B&L, making it more valueable.
In an IPO the company is worth less because it has to support itself. No distribution or manufacturing benefits, no job cuts. The only benefit to earnings would be the reduction to debt, which would reduce interest expense and improve cash flows, but not improve profitability.
The bidding process gave potential investors a look under the hood and told WP what people thought B&L was worth (ish). I still think an sale would be more profitable for WP than an IPO, though I dont think 10bn is in the cards...I wouldn't be surprised if a sale brough in around 8bn and an IPO brought approximately 7.6 (on the high side).