"isn't really"... doesn't mean none
There might be the odd FinTech. Btw MyCard2Go I wouldn't class as a Fintech. Revolut, Monzo, Monese, Starling, N26, Tandem, bunq, boon (maybe Fidor) and so on: They are FinTechs and they are almost exclusively on the MasterCard platform.
Monese used to have Visa Debit, Revolut used to mainly hand out Visa Prepaid. But they've both now almost exclusively switched to MasterCard. The Revolut virtual cards still seem to be Visa only...
As kkrdvc mentioned fees is one big factor. The other is agility: MasterCard is much more interested in connecting with the FinTechs directly and offering technology that Visa just isn't able to deliver. For example they have dedicated staff to assist in the integration on the new platforms. Visa seems to be much more comfortable so far with the big banks, but they've also realised they have a need to catch up.
Look at the mobile payment launches in 2018: it was mainly a "MasterCard party". Visa hasn't been integrated with the Sparkasse app yet, Revolut only supports MasterCard and Maestro and with Apple Pay certain banks only support MasterCard.