Case against bishops lost amid the hysteria
Why didn't the Pope accept the resignations of Auxiliary Bishops Walsh and Field? The answer is that in the case of Bishop Field it wasn't justified, and in the case of Bishop Walsh it was a 50/50 call.
It is true that these two men were named in the Murphy Report, but this fact alone does not justify calls for their resignations. Being named is not the same thing as being denounced and neither man is denounced in the report, whereas other auxiliary bishops from the period under investigation -- 1975 to 2004 -- are, namely Bishops O'Mahony, Kavanagh and Murray.
Let's take a slightly closer look at the case of Bishop Raymond Field. The report doesn't criticise him in any significant way and therefore he is not remotely in the same category as say, Kavanagh or O'Mahony, who very much belong to the era of cover-up.