The requirements that Kura sets in terms of operators make it harder for smaller ones to win the contracts since the level of infrastructure, staffing and the amount of boxes that an operator must tick makes it more difficult for the smaller operator where staff may do more than one role whereas larger companies can spread such costs over the wider company with dedicated staff.
For example I heard when they tendered for another contract elsewhere in the country, they wanted a publicly accessible lost property division, a dedicated help desk / back office provision with dedicated staff, £12m of public liability insurance, high level disaster recovery policies and they had a fairly sharp focus on newer vehicles as well. Some of these things are easier for a larger company with bigger infrastructure and publicly accessible Town based facilities to meet than the smaller operator.
Also I'm not sure the contracts are so favourable for operators anyway. Kura apparently train the drivers to their own operating proceses rather than the companies and there was even talk on the Ipswich school contract that prior to drivers starting they had to do route practice laps and be monitored by Kura who would approve if they drove the route right. They also need to install infrastructure on the bus to support the Kura app and whilst the operator will be held liable for delays etc, if students damage the vehicle Kura or the school cannot be held liable under any circumstance. It does make the contracts seem a bit one sided and I'm not too sure many independent operators would like being told how to run a bus service by a technology company that has never run bus services itself.