I used them both extensively, and here are the main reasons I can think of:

- The event loop in JS is invisible and implicit. V8 proved it can be done without paying a cost for it, and in fact most real life python projects are using uvloop because it's faster than asyncio default loop. JS dev don't think of the loop at all, because it's always been there. They don't have to chose a loop, or thinking about its lifecycle or scheduling. The API doesn't show the loop at all.

- Asynchronous functions in JS are scheduled automatically. On python, calling a coroutine function does...nothing. You have to either await it, or pass it to something like asyncio.create_task(). The later is not only verbose, it's not intuitive.

- Async JS functions can be called from sync functions transparently. It just returns a Promise after all, and you can use good old callbacks. Instantiating a Python coroutine does... nothing as we said. You need to schedule it AND await it. If you don't, it may or may not be executed. Which is why asyncio.gather() and co are to be used in python. Most people don't know that, and even if you know, it's verbose, and you can forget. All that, again, because using the event loop must be explicit. That's one thing TaskGroup from trio will help with in the next Python versions...

- the early asyncio API sucked. The new one is ok, asyncio.run() and create_task() with implicit loop is a huge improvement. But you better use 3.7 at least. And you have to think about all the options for awaiting: https://stackoverflow.com/questions/42231161/asyncio-gather-...

- asyncio tutorials and docs are not great, people have no idea how to use it. Since it's more complex, it compounds.

E.G, if you use await:

With node v14.8+:

await async_func(params)

With python 3.7+:

import asyncio

async def main():
# no top level await, it must happen in a loop
await async_func(params)

asyncio.run(main) # explicit loop, but easy one thanks to 3.7

E.G, deep inside functions calls, but no await:

With node:

...
async_func(params)

With python 3.7+:

...
# async_func(params) alone would do nothing
res = asyncio.create_task(async_func(params))

...

# you MAY get away with not using gather() or wait()
# but you also may get "coroutine is never awaited"
# RuntimeWarning: coroutine 'async_func' was never awaited
asyncio.gather(res)

Of course, you could use "run_until_complete()", but then you would be blocking. Which is just not possible in JS, there is one way to do it, and it's always non blocking and easy. Ironic, isn't it? Beside, which Python dev knows all this? I'm guessing most readers of this post will have heard of it for the first time.

Python is my favorite language, and I can live with the explicit loop, but explicit scheduling is ridiculous. Just run the damn coroutine, I'm not instantiating it for the beauty of it. If I want a lazy construct, I can always make a factory.

Now, thanks to the trio nursery concept, we will get TaskGroup in the next release (also you can already use them with anyio):

async with asyncio.TaskGroup() as tg:
tg.start_soon(async_func, params)

Which, while still verbose, is way better:

- no gather or wait. Schedule it, it will run or be cleaned up.

- no need to chose an awaiting strat, or learn about a 1000 things. This works for every cases. Wanna use it in a sync call ? Pass the tg reference in it.

- lifecycle is cleanly scoped, a real problem with a lot of async code (including in JS, where it doesn't have a clean solution)