Since Loreal is a cosmetics company, the slogan 'Because you're worth it.' makes potential customers feel valued and that they deserve good quality of cosmetic like the ones in Loreal. This appeals to customers to purchase products from Loreal.
The tone is that Pepsi is the authority on cool and they know what people want. If you don't choose Pepsi as well, then you must be the old generation. This is the new thing - using fear of not fitting in to push people into buying product.