Probate attorneys should know this, but they often (usually?) are not knowledgeable enough about the income tax aspects.

Many CPAs do not work on estate/trust income taxes.

Since there were no beneficiaries on the IRA, the estate gets the money and all would be taxable in the year of death/distribution. The money is not "rolled over" to the estate account; it is distributed and taxable.

Estates pay income tax at higher rates than individuals, and 100% would be taxable to the estate rather than split amongst beneficiaries. If you can get most of the money distributed before the fiscal year end of the estate, you can pass this income through to the beneficiaries instead of taxing it to the estate, but the estate must be terminated.