Apple has only just introduced the ability to transfer everything from one iPhone to another directly. You still infamously can't transfer many common data sets onto or off those phones through standard protocols, and Apple's proprietary software seems to have a poor track record, again pushing users towards iCloud.

If the particular app you have in mind doesn't support that feature (most of the ones I use do), that's not Apple's fault.

And the fact that Apple's entire system uses a proprietary storage scheme and doesn't support standard protocols other than for a few specific cases like photos clearly is a decision that Apple has deliberately made.

IME, wirelessly iTunes can be flaky, though better than in the past. My direct personal experience is that if you use a wire, as stated, it's flawless.