Roth conversion is taxable but it is being included in the Modified AGI when determining by healthcare credit. Why? The money was moved into a retirement account.

The taxable amount of a Roth conversion is included in AGI and there is no subtraction of this taxable amount when calculating the MAGI for any purpose other than the MAGI making a Roth IRA contribution.  In particular, there is no such subtraction for calculating the MAGI for the purpose of determining Premium Tax Credits on Form 8962.  This is the way Congress wrote the tax code.