There are dual CPU socket 2011 motherboards, here is one EVGA Classified SR-X 270-SE-W888-KR LGA 2011 Intel C606 SATA 6Gb/s USB 3.0 HPTX Intel Motherboard
- and here is a list of more http://www.newegg.com/Product/ProductList.aspx?Submit=ENE&N=100007629%20600288062&IsNodeId=1&name=Dual%20LGA%202011
they are pricey and can only be used with Xeon E-5 processors.
Dual CPU motherboards are not currently made for standard processors for a few reasons; price, standard CPU's are incapable of working in unison (without severe modding) but mostly need - sure it may help your folding/bit-mining/BOINCing/vid editing to have a bazillion cores running (sure won't help the electric bill though) but for the 'standard' computer user, there just isn't the demand to design one. Even enthusiasts are hard pressed to justify the expense to return ratio of the Dual CPU mobos. I know in my case, cost isn't an issue but I still don't own one - although I do often consider whether I can justify the expense, so far, NOPE.
My take on the issue