Ok, going against the grain here.
the “why”is not about language development so much as natural curiosity.
curiosity is hugely important for the development of skills, intelligence and its crucial for raising kids that love to learn and see learning as a lifetime skill. This is a massive gift to promote in your child that will help them become interesting people who are interested in others, maximise their potential and ensure flexibility to adapt to changing circumstances as adults.
as an employer I always looked for people who showed curiosity , and confidence (a self reliance type, can do attitude). With that, pretty much everything else can be learnt . As a parent I would always try to answer and actively encourage curiosity by often asking them why do you think , even when they’d not asked me a why. But, hey, I love teaching anyway so loved this stage of childhood. Both kids have grown up to love learning and have generally been able to make the most of their skills and continued growth
I have seen parents shut down a child’s natural sponge like curiosity in a few thoughtless words. Please don’t close down the curiosity. It’ll only take a few times of a child feeling they’re in the wrong for asking “why” to get to a place where they don’t bother asking anymore.
The way is to answer as best you can - or better still, as other people have suggested, turn it into a full chance to explore with a “why do you think, or what do you think”…
if you do have a child who is just exploring how to get your attention or wind you up by repeating “why” in every breath , it’s probably cos you have dismissed it - if you do answer and make it part of a longer conversation, they’ll soon stop using it as a quick attention seeking device given it’ll be turned into a longer lesson 🤣🤣
if you are tired or worn out- park the question. Tell the child they’ve asked a particularly good question and you need time to think…then at a later point when less busy, tired etc , sit down and go back to the question- they’ve maybe lost interest by then but at least you didn’t just shut them up and close them down. Always reward and acknowledge curiosity and don’t dismiss, ignore, etc.