I'm sure it's mostly for the name. Full disclosure: I have never had spotted dick.
It does sound good but I've just never been offered it. Maybe it's a regional thing? Britain, even just England is really a mass of different places all crammed together and all insisting we are English! I'm beginning to suspect two things:
1) Claiming to be English and an authority is a waste of time. Whatever you think is English most others anywhere else will disagree and will fight you in social media comments.*
2) That Peterborough is missing out on spotted dick
*'Literally everyone in Britain thinks Yorkshire Tea is the best!' - Yorkshirelord626
'How dare you tell Americans to make tea like that you wretched **** ****er . TEA POT! Bags are the work of Satan!'
'Yorkshire Tea is nice but Earl Grey would like a word...'
'Darjeeling. Mike drop ****** ******s. Did you scumbags go to ETON or something???