That's not true, although I assume it may be harder to water-proof devices with each possible opening in the chassis.
There are some water-resistant phones with a headphone jack and an IP68 rating even. The LG V30 for example is a beast. Semi-regular usage on rainy days works without any issues. Even using it as a flashlight it survived 30min of pouring rain. I had to wait for the USB-C port to dry up to charge it after getting home, but it still survived without any damage whatsoever.
Other phones that are both water-resistant and have a jack [1]:
* Pixel 3a
* Galaxy S10
* Huawei P30
* and a lot more
If I remember correctly, Apple tried to justify its removal due to its size and water-resistance. I wonder when (not if) Apple will remove the power plug due to "water-resistance" and insist on using Qi charging (even though it has worse efficiency[2]) and cloud services instead of transferring data via cable.
[1]: https://www.androidauthority.com/phones-with-headphone-jack-...
[2]: https://www.wirelesspowerconsortium.com/data/downloadables/1...
