You can blame IRS because their Quickie Guidance, reacting to Media Guidance, initially said that decedent payments should be returned.  But blame yourself also, because by January the 1040 Instructions had been published:

Form 1040 Instructions, Page 56

Generally, you are eligible to claim
the recovery rebate credit if in 2020 you
were a U.S. citizen or U.S. resident alien,
weren't a dependent of another taxpayer,
and have a valid social security
number. This includes someone who
died in 2020, if you are preparing a return
for that person.