Let me answer you honestly and in depth:

Why? Why not? If I am alive, I may as well make an effort, since I have a finite time to do so. It's fun. It's a challenge.

I know a couple of men in their 50s, one is relatively wealthy (some tens of millions of dollars), and I have often seen him on top of a machine with a wrench in his hand at 6am. Sometimes it's 3am. He starts a new company every year or two and adds it to his holdings. He owns farms and factories, and runs all of them personally. (it baffles me that he has enough time) I know another man who's relatively broke (owns his house, not much else) and says he is too old to try any new ventures. I suspect a large reason for their wealth disparity is their attitude disparity.

Money is also more than the ability to acquire toys. Money is power, and money is freedom. Money is time. Money can pay other people to save you time. You can save thousands of hours over the course of your life paying other people to mow your lawn, wash your car, paint your house, repair your engine, and re-tile your bathroom.

Money can buy you citizenship anywhere you want, and if war comes, you can just pay to fly away.

Money can establish schools, medical research orgs, and human rights charities. Money can buy media and reshape politics, or it can pay for scientific instruments that have no other funding, and it can secure the future for people (or other things) you care about. Paul Allen built a telescope array, the world's largest airplane, the living computer museum, a cell research institute and a brain research institute, and a ton of other fantastic stuff that would otherwise have no funding.

Howard Hughes Medical Institute is still one of the wealthiest charities in the world, he's been dead for 50 years and we are all still benefiting. That wouldn't be the case if he spent it all on yachts and mansions.

Money can keep an old-growth forest from turning into an apartment complex.

Money also makes all kinds of new things possible, and allows you to do things "The Right Way", i.e. to overengineer for the sake of beauty and reliability, cost be damned. Money can replace a cinderblock and plywood hovel with marble and oak. Money can build you a house that can ignore tornadoes and earthquakes. Money can pay engineers and machinists to create things that would never be commercially produced.

Money means I can work on what I want to work on: difficult and time-consuming things.

Money means I can buy the local schools all of the equipment I think the kids should have, and more importantly, I could pay for staff to make that equipment useful and not just sit in storage because none of the teachers understand telescopes or computers or 3D printers.

I could pay for our town to have a planetarium. On that note, if I were rich enough, I could embarass Zeiss and build the most ridiculous optical planetarium projector ever known.

Like it or not, money is also respect, awe even. I want to be the husband most wives could only dream of, in terms of success.

I want to buy my children education they can't get at school, by doing things with them the school cannot afford to do.

Money means you can participate in expensive hobbies that introduce you to people that you'd otherwise never meet. Those people are often interesting.

I want to set an example for my fellow citizen, and show them that it doesn't matter that we live in a shitty town in the middle of nowhere, if you just refuse to concede that our disadvantages cripple us, you can still win. We're human beings after all.

I don't even own a house yet, but I started another company 6 months ago, and this time I have no business partners to blame and no outside investors. It's all me. Moving to a small town in the middle of nowhere on the other side of the world just makes it more fun, it's life on a higher difficulty setting. I relish the challenge.

I could probably rant about this for hours, it's not that we need the money, it's that without it, so much less is possible.

We (humans) just achieved fusion, and that machine cost billions. It wasn't a toy. Money is the power to build the future.