I agree with a lot of the responses above. We are all free to do this for our own reasons, and it offers a great deal of flexibility and variety, so I don't throw shade to anyone who does it for their own reasons.
The experiences can be a nice way to supplement your social life or do/try things you may not normally be able to afford otherwise. I've been a shopper about 15 years and when I realize that some of the fees are still THE SAME despite inflation, minimum wage increases, additional requirements, etc, colokate summed it up - hobby shoppers drag down the fees.
I do some merchandising projects and I will not take rock bottom fees that undercut other merchandisers in my area. I also will not do work for companies that post billions in profits and want to have shoppers gather intel for them for $7 and a $1 reimbursement and $2 of gas. A lot of new shoppers don't realize how fees or bonuses work, and they don't realize their own overhead involved in doing a shop. More than likely, you will need to have a phone, data/wifi plan, a vehicle, pay your own taxes, and of course, your time.
We are all "labor" and not the elites in this country. The only way labor has advanced their pay, benefits and working conditions, has been to organize and display solidarity. I don't expect that to happen in this industry anytime soon, so I stick to my own principles and protect my bottom line.