From a strictly utilitarian perspective, there are good reasons to spend time with loved ones, cultivate emotional bonds, and pursue personal hobbies:
Your own well-being counts too. A utilitarian doesn’t just care about the welfare of strangers. They care about everyone’s welfare, including their own. If living altruistically leaves you miserable, then by utilitarian standards that’s a loss of value, not a gain.
Not all goods are fungible. Money can be redirected to different causes, but emotional attachments and sources of intrinsic motivation aren’t as transferable. So it doesn’t make sense for a utilitarian to demand that people rewire these aspects of themselves. Human being just don’t work that way.
Burnout is real. A person who devotes themselves single-mindedly to a cause might be admirable, but they risk exhaustion and loss of motivation in the long run. And conversely, a person who feels joy about life will be more motivated to continue working towards the ends they care about.
Role models can inspire others. If utilitarianism looks unpleasant, fewer people will want to adopt it for themselves. But if people see utilitarians living rich, balanced lives, they’re more likely to be inspired by example and join in.
That said, I don’t think EA is committed to utilitarianism. Instead, I think EA is more centered around beneficentrism, the idea that it’s really important to help others. The difference is that beneficentrism doesn’t entail maximizing the world’s total welfare. Rather, it’s consistent with this view to be partial to one’s family and loved ones and to have carveouts for one’s own personal projects.
Not all capabilities matter. For example, the capability to burp really loudly is not a morally important one. If we were trying to improve the world, trying to give people the capability to burp loudly is not in the top 1000 list of things I’d suggest prioritizing.
And plausibly, the reason why this capability doesn’t matter is because it doesn’t promote wellbeing. And more generally, this might be true of any capability. The reason why the capability to get an education or access healthcare are important is precisely because they reliably lead to people living better lives.