Elimination of the headphone jack makes sense, any opening is a potential weak spot, and a place to allow debris intrusion or water intrusion.
The iPads are not water or dust resistant in any way. On the iPhones you can argue that since they are indeed water resistant it's easier to seal it reliably if it has less ports. There is no need to remove the port on the iPad as it isn't a weak spot to begin with. You know what is a weak spot though? Instead of having two connectors where you plug headphones and the charger in, now you have one port where you plug both in - thus the single port now gets way more plugging in/out cycles than if you could distribute that over two ports. That's a problem with USB-C especially since those ports absolutely do fail. Just ask owners of USB-C-only Macbooks where many had their ports fail prematurely. The reports are mostly for older 2016/2017 models, I can't say if that's because they are now so old that the ports start breaking or if those had a flawed design.
In any case, whatever "potential weak spot" you are talking about, if you submerge the iPad in water it's going to die whether it has a headphone jack or not. That makes no difference. And if you splash a bit of water on the display by accident, whether there is just a USB-C port or a headphone jack next to it won't make a difference either. If the water gets into the device with the USB-C port the iPad is dead as well.
This implies that apple removed the headphone jack to pressure people towards AirPods (despite Lightning EarPods being included for four years until the iPhone 11).
For the iPhones I can see the reasoning that it's easier to seal them more reliably with less ports, since these are water and dust resistant. It's still possible to make water resistant phones and equip them with a headphone jack, but still, at least there is a valid reasoning from a technical point of view. This does not apply to the iPad as it is not resistant to water or dust in any way.
The included headphones aren't a sign for anything. It was just normal back then to include headphones with smartphones. Nowadays phones no longer come with a charger either, but that isn't a sign that Apple wants to sell more chargers, it's just the industry standard changing.
Apple knows that if you buy an iPad today that doesn't have a headphone jack, naturally you will wonder what you need to do to get headphones working and how much it costs. And then you will find that the Airpods 2 are amongst the cheapest reliable bluetooth headphones and you're already standing in an Apple Store with the iPad box in your hand and the employee conveniently offers to add the Airpods to your purchase.
Apple doesn't need to pressure anyone to do anything, they have marketing for that and the fact that most of their products are actually very decent and mostly "it just works". So when Apple removes the headphone jack from the iPad it's a fact that it will increase Airpods sales, we all know they are the most popular bluetooth headphones in the world.
I myself bought Airpods despite using them mostly with my Pixel that doesn't have a headphone jack either, simply because the Airpods work better on an Android than any other bluetooth headphones for under 100 bucks. Good quality bluetooth headphones that are cheaper than the Airpods 2 just do not exist, I had such cheap ones from Shure and they died within a year and battery life was about 4 hours from the start. At least the Airpods live a good 2-3 years before the battery starts giving out.
