Its more costly and vastly more negative from a PR perspective, for McDonalds to force franchisees to change ice cream machinery vendors.

Same thing for Taylor upgrading their own machines - with the added cost that they don't have any goodwill to start.

There's an added incentive here that McD wants the legal shield up at all times - they are incentivized to keep machine error rate very low, to the cost of $$ in sales lost.

Consumers greatly benefit from it - we get worse availability of ice cream when we walk in, and we are paying slightly more in menu prices, but the risk of getting poisoned from eating ice cream at McD ends up extremely low.

And that's where the intrigue and accusations of foul play are coming in. It seems like McD's has mandated this model of Machine and Taylor agreed to make it worse (they supply better machines without these issues to other fast food chains). Taylor profits from the service calls and I'd bet some McD's exec are getting kickbacks to keep it that way (by mandating a worse machine that makes franchise owners less money). The Kytch device came along and upset that status quo.