It's funny that selling the company was their priority, and that they had to hire an investment bank to look for funders.
Bankers have a much wider network of potential investors than founders, and they can also run the process much more efficiently. Raising $141M is different from raising $14.1M, it gets way more complex. And at that amount / valuation, what can be a financing can quickly turn into an acquisition, think what happened to Cruise Automation.
Frequently the bankers do a principal investment in the same round they are raising for the company, to show that they have skin in the game, but also to position themselves for a potential IPO or M&A transaction (which is the lucrative part, you get 2-3% of the total consideration).
Qatalyst is well known in the Valley, another firm is Allen & Co. Both companies do principal investments, and so do the bulge bracket firms like GS, JPM and MS. GS put money into Uber.
So it's probably not "had to hire" but "decided to hire", and a perfectly common practice.