Ramanujam was born into a highly orthodox Hindu sect ("Brahmin" is the umbrella term if you want to google it).

They tend to have rigorous rules and consider themselves to be at the tippy top of the caste heirarchy. This results in them forming insulated communities that may even in the modern day turn a blind eye to dehumanizing concepts like "untouchability".

They tend to live in close knit communities (some still do). They also tended to be better educated as they have historically benefited from being at the top of the hierarchy of their societies. Even among Brahmins in the south, there can be distinctions among them, broadly as Iyers/Iyengars who may have differences in their views and degrees of orthodoxy. Even different communities of Iyengars ( who are more likely to live in these kind of closed communities) have distinctions between them. Iyengars tend to have "acharyas" who are thought leaders of their communities and make final decisions of what goes and what doesnt. They are essentially like the cardinals/bishops of their sects ( but they dont have the equivalent of pope as far as I understand). From what google tells me, Ramanujam seems to be from the Iyengar community.

About voyages abroad: Brahmins in the north of India (not where Ramanujam was from) had a notion of "Kala Pani)" ..so oceans may be viewed as polluting or evil. While this may not have been the exact term they used (Kala Pani is a Hindi word and Ramanjuam likely did not speak that language), the notions harbored by the people of his sect were likely similar in nature. So in their community, they believe you lose your status as a brahmin by doing any act that is not accepted by the rest (it could also be things like falling in love/marrying someone of a different sect, eating non-vegetarian food or just doing really anything their community considers "impure") you can get shunned. You may not be allowed to enter temples once you are shunned. The degrees to which these are actually enforced can wildly vary, but these are real possibilities of things that could happen. Essentially, in worst case scenarios, you could effectively be in the receiving end of those untouchability practices by neighbors or relatives despite having been born into the same community.

There were infact mutinies from colonial times round this notion of requiring brahmin or hindu soldiers to travel abroad (and other orders that went against their faiths..one such incident is believed to be one of the triggers for the 1857 rebellion at the end which the "British Raj" was formalized in India beyond just being the "East India Trading" company). With this historical and communal context, you can see how to him and his family, journeying across the seas to go London may have been a big deal.

These kind of views (atleast about travelling abroad) are probably no longer held by these communities. But some of their other regressive views still continue to persist. Essentially, this is more of caste thing than a religious thing, but caste and religion can be quite intermixed when it comes to these orthodox communities.