Single people have more risk. DP and I both work. When DP was made redundant, we still had my salary coming in. Single friend who was made redundant was only entitled to about £70 a week unemployment benefit. It is far easier financially as a couple. It spreads the financial risk, and it is cheaper living as a couple.
It's nice that a coupled-up person finally gets this! 
And when I participate in this discussion, I participate as a truly single person - nit just someone who's coupled but just not living with my partner
There.Is.No.One.Else.
I once took on a high-stress, high performance job. I got paid a bit extra but as I was working long days, 6 days a week, that extra money was not-quite enough to pay for a cleaner once a fortnight & a gardener once every 6 weeks or so.
But the thing that I found even more difficult was the lack of domestic emotional support from a committed intimate domestic partner. There was no-one to go home to, who would (mostly) revive in me the idea that I was an OK person, and help me to find my nice ordinary self, who showed me that - whatever difficult decisions I was having to make at work - I was still loveable/likeable. No shoulder to cry on, and no-one whom I could love & care about.
Yes, I have friends! Of course. And good colleagues, and family.
But no-one for whom I come first. It made doing a tough job very very tough in a way that those of you with [good] partnerships have vbery little idea about. I do that day in, day out.
I solved it by spending yet more money: I bought in a therapist - I went weekly, as a way of getting a safe place to offload & think things through, without fear of over-burdening friends or colleagues. I received mostly unconditional positive regard through person-centred counselling (it's a standard therapeutic approach). This was particularly necessary when I was being bullied in my job (I may have been in charge in title, but there was a colleague who resisted & fought that via bullying).
I worked through some issues, but when I look back, I realise that part of what I needed was the feeling of having intimate/confidential emotional support. A therapist is not a loving partner - of course! But she offered me a shadow of that feeling of someone being 'on my side.'
Being single can take an emotional toll, when you have to face everything essentially on your own.