15 Years of OsmAnd

1. Users will use low quality SD cards (either remarked as a fast card, and sold cheaper than most fast cards, or deliberately because they want high volume storage for small money), and then complain about the phone being slow. Fine for a budget phone, not so good for a premium phone.
2. Users will change the SD card, and then complain that their phone has lost data, because things they used to have "on their phone" have gone missing. This will, again, be blamed on the phone, and the user is unlikely to come back and admit it was a result of changing SD card - which makes the phone look bad.
3. If you're building to a price point, there's storage capacities that are unsaleable - if you're looking at phones under £200, you're unlikely to be willing to pay an extra £100 for a phone with 1 TiB of storage instead of 128 GiB. If you're looking at the base model costing £1,000 (or more) for 256 GiB, paying an extra £300 to have 1 TiB of fast storage feels more reasonable. As a consequence, low end phones aren't sold with big internal storage, whereas high end phones are.

And, of course, there's the thing where someone who's paid £150 for a phone is less likely to be willing to pay £50/month for unlimited data, whereas someone spending £1,000 on a phone might well pay for unlimited data, and thus be more willing to rely on cloud storage for bulk data like photos and videos.