Because, if you have this today, you will get more when VS2010 arrives:
Here’s how subscription levels will transition:
If you have this active subscription on March 22, 2010:
…then your subscription will become this:
…and you’ll get everything you had before, plus:
Visual Studio Team System Team Suite with MSDN Premium
Visual Studio 2010 Ultimate with MSDN
Visual Studio 2010 Ultimate, Team Foundation Server 2010 + CAL
Visual Studio Team System editions with MSDN Premium (Architecture, Database, Development, Test)
Visual Studio Professional with MSDN Premium
Visual Studio 2010 Premium with MSDN
Visual Studio 2010 Premium, Team Foundation Server 2010 + CAL
Visual Studio Professional with MSDN Professional
Visual Studio 2010 Professional with MSDN
Visual Studio 2010 Professional, Team Foundation Server 2010 + CAL
Visual Studio Professional with MSDN Embedded
Visual Studio 2010 Professional with MSDN Embedded
Visual Studio 2010 Professional
MSDN Operating Systems
See details of the Ultimate Offer for devs
And then there are the Windows Azure Platform benefits! https://msdn.microsoft.com/en-gb/subscriptions/ee461076.aspx