ESA3 Change of circumstances - Help!

I have recently had my (CB)ESA reassessed and it has been awarded. I was in receipt of (IR)ESA but this was reduced when my occupational pension started after being retired due to ill-health.
I also recently got married and when I telephoned the ESA helpline to inform them, they told me that I would still be entitled to the (CB)ESA as I had paid enough NI contributions in the past.
I have now been sent a ESA3 form to complete my new details. The compliment slip attached asked me to "fill in my new details", so I sent it back with just my new name. It was returned, asking me to put my husbands details in and to complete the form in full too.
If I am only in receipt of (CB)ESA and do not want to be re-assessed for (IR)ESA as my husband is working, then why do I have to fill out this form in full?

Any help/info would be greatly appreciated.