AWS certifications are not "useless". They are an industry standard, kind of like being a CNA (Certified Novell Administrator) back in the day.
If your company wants to participate as an AWS Solution Provider, there are hard requirements for the number of staff with AWS certifications. Most Fortune 500s will only work with AWS Solution Providers, so there is a huge incentive for consulting companies to encourage or even require their employees to become certified. This can involve holding back promotions, paying for test fees, allowing the employee to study on company time, bonuses and any number of "carrots".
Also, AWS certifications expire in 3 years from the date of the test pass which I think is a good timeframe, given the historical rate of change.