We can consider the hair as predominated by Vata, and the head as the place of Kapha. Higher Pitta means that hair goes through its lifecycle quicker - and falls off.
In short, a Vata predominant substance (hair) situated in a Kapha predominant region (head) is falling off due to excess Pitta.
In current environment, we see variation in Kapha dosha due to rapid changes in temperature, moisture from ACs, use of chemicals on scalp etc. This can cause starvation of the hair roots. For example, low Kapha means reduced nutrition to the hair roots and high Kapha means that nutrition is blocked and not absorbed.
These issues cannot be mitigated by just adding in nutrition - because it just wont be absorbed. This is why balancing all the three doshas is very important for managing hair quality.