Hey, my field here (still in pharm school, but I'll specialize in delivery).

1. Getting an approval is a long, hard and expensive process, all things that you want to avoid. On top of that, a patent expires after a while, so other companies who didn't spend money on the research process can manifacture the med and sell it (the so-called generic drugs), BUT you can extend the patent if you re-patent it in a different-enough formulation.

2. Each route has its advantages and disadvantages, and the main ones are actually different enough to just choose in advance depending on the effect you need (instant vs slow release, for instance). However, there are A LOT of finer delivery methods which can be used, that can modulate the release (targeting something like a tumor or releasing through a precise pattern like concerta / ritalin XR, not to mention advanced methods that involves heat or other external stimuli).

Now, given 1) and 2), you can understand how the first try for at least a general method, the ones that fits the reason why it's being developed, patent and get the AIC (Italian for Autorizzazione all'Immissione in Commercio, don't know the English term, basically authorization to sell it) as soon as possible, after refining the chosen one.

After it's on sale, they'll find a way to repurpose or formulate it differently, maybe trying for an XR version, and testing for different delivery methods, which will be patented right before the other one expires. They calculate it to day precision.