The business logic was quite simple. They had a fleet of (numbers made up) 30 trains that were approaching their mid-life refit. At the same time, they intended to add new services that would require (another made up number) 5 additional trains. Complicating matters, the existing fleet couldn't operate the new services through not having the necessary equipment.
So, the options were:
- Refit exisitng fleet and not operate the new services
- Refit existing fleet and buy a small sub-fleet of new trains to operate the new services
- Buy a fleet of new trains and refit a small residual sub-fleet of old trains
- Buy a completely new fleet of trains
Option 1 had the lowest capital cost but wouldn't help to grow the business. Option 4 had the highest capital cost. Option 2 had the second-lowest capital cost but meant that the per-unit cost of the new fleet would be much higher, and they would be up a creek if one of the new fleet went out of serivce.
So option 3 makes the most sense and that's what they've done. (I know, more of that logic and common sense.)