Landing toe first is a tell tale sign of heel pain (indicative of navicular , but not all heel pain equals navicular). It's also caused by imbalanced trimiming. Long toes esp. create a flight pattern that makes it hard to land heel first, even if there is no heel pain initially.
Landing toe first causes a lot of chain reactions that cumulate over time. It's hard on the tendons, is the landing that transmits the most shock up the leg (and damages the navicular bone) and tends to cause separation of the white line at the toe. It also means the frog doesn't get enough stimulation and that makes it easier for thrush to set up.
That's the quickest, easiest explanation.