I have been hiring software engineers for many years. One thing that has become clear to me, is that many engineers look at their next role primarily as a learning opportunity, for example they want to learn a new programming language or cloud technology.

Engineers are smart people, and they will select a role based upon what they can add to their resume, to make themselves even more attractive for subsequent roles.

As a hiring manager you need to be aware of this. Your objective as an engineering manager is not to develop rounded individuals, but to ship product. You are not running a university. The only exception to this should be when you are hiring junior engineers, for example new graduates.

However, so long as your agenda (to ship product) is aligned with your engineering candidates (to learn cool new tech), you should be fine.

One final thought: be aware that engineers will push for certain new tech to be adopted, not because it's the best thing for the business per se, but because it's something they want to learn on your dime. Always challenge on this, and only accept the risk of new tech based on very compelling engineering reasons.