People have already added a bunch of great replies, so I'll just be brief:
A) You can do both. ^^ My day job is an "essential" profession in the medical field, and I spend pretty much all the rest of my time making funny drawings and comics and animation that no one even pays for, let alone "needs". And it works for me.
B)
And those people (assuming they aren't artists themselves, which is entirely possible) need artists.
When the inventor is in engineering school, whose music are they going to listen to while they study?
When the philosopher is writing their book, whose stories are going to inform the way they compose their thoughts and establish themes?
When the leader is trying to connect with their audience, who is going to make sure they look their best in front of the camera, and display their message in an aesthetic, informative way? Who's going to create logos and slogans for them to catch people's attention??
Art is a HUGE part of life. I'd even bet that human life as we know it has never existed without art...the problem is, nowadays we take it for granted. Logos simply exist, videos are simply posted, books are just published, music is just downloaded. No one considers where it comes from, or how much of a marvel it is that so much art is available to us 24/7.
I guarantee you, if the work of every 'unneeded' artist on the planet suddenly vanished, EVERYONE would notice. And the world would be a much duller, sadder, more depressing place than it already appears to be.