JWST reveals its first direct image discovery of an exoplanet

The JWST is a marvel of engineering. It is also a machine designed around the restrictions of what the most powerful rockets of the 1990's were capable of. Just imagine how capable future telescopes will be now that we have multiple super-heavy launch vehicles with cavernous payload fairings in development.

it's hard to commit to building JWST type of payload around a non-yet proven launcher. you'd want to wait until the "in development" becomes proven before planning to launch some decadal planned mission.

Ariane 5 seems pretty proven to me :D