Exactly, casinos are a form of business, and like all business models, it has been created to make money from customers. If the marketing team has decided to land bonus events it is understandable to see some wagering requirements to be eligible. The only exception can be the early days when the new casino has no user base so it makes sense to get some freebies.
Marketing model for legit business must have good budget at start as a good and deep budget is necessary to make an acceptable long lasting marketing plan that is helpful to gain enough data and potentially success from marketing.
However after spending initial budget, a business company must receive enough positive results from marketing which should be reflected on website traffics, organic growth of customers and their money spent on the site to use products, play games, bet ... If there is good positive net income from input and output money (output will be partially spent for marketing), the company will continue their marketing and even can expand it bigger or launching new types of marketing.