I worked at a company with this disease before. The system was an abomination of vastly different technologies over the years stitched together loosely.
Development was slowed substantially by having such a mess and the company couldn't move fast enough to compete so the startup died. Usually tech isn't the reason for a startup's death. In this case, it was.
Sure. That's one of the responsibilities of a team lead: to help team members to work and gradually build up their CVs. I want my team to experiment new stuff and learn while working. But I also want to limit the risk boundary. The whole reason why younger people are leaving dinosaur companies is that no one in management layer lets juniors experiment and fail. End of the day junior devs also want to improve and develop.
Otherwise the solution is to crunch-time people into oblivion and and quickly replace them when they burn out. Not exactly sustainable
A balance has to be achieved. Obviously we can't sit around all day rewriting simple things in our pet language of the week...but employers need to understand that a good developer will not let their resume atrophy.
The days of the twenty-five year stint followed by a gold watch and a pension are over...you simply cannot put your employer's needs ahead of your own anymore.
Some companies require managers to aid in the technical development of employees, some don't. Some provide a lot of latitude in how that's done, some don't.
It's not about what a company "requires". It's about the moral duty you take on when you manage people.
If a company decides that technical development of engineers is good for retaining engineers and you as a manager refuse to do that, then no moral argument is going to help you when you get dinged in your performance review.
edit: Upon rereading the thread, I suspect that we may agree more than we disagree. My comment was directed at asknthrow's comment and I wanted to make the point (which other posters have more eloquently made in the meantime) that if technical development is part of your job as manager, you don't have a choice in the matter and your job is not just "to lead the team in the most effective direction in order to fulfil business objectives" (to quote asknthrow).
And when some new tech comes up then the business hires shiny new people because the people working for them haven't "kept up".
So, you have to strike a balance between getting stuff done and taking care of your people in terms of professional development and growth.
It's ok, most organizations fail at it. The "90% of everything is crap" rule applies to managers as well.
Your job as team lead, however, is pretty clear. You lead a team to create value for your organization. Professional development is an obvious tool in that toolbox. Finding ways to limit or restrict exploratory development in order to reduce risk is another.
aka managing your own career. Don't wait for a company to do that for you, its not 1955 anymore.