The reason for the above is because "Bussetsu Muryoju-kyo Sutra" preaches that Amida Nyorai's vows (Forty eight vows) are admitted by various Buddha.
その理由は、『無量寿経仏説無量寿経』に阿弥陀如来の願（四十八願）は諸仏に認められていると説かれている事に依る。