Why

1. To protect against SV replay
2. To deny SV the transaction volume to appear as a chain in use

How

A Satoshi from coins mined after the fork has to be sent to every address that has a balance greater than zero. The UXTO database can be queried for the set of adresses that satisfy this criteria.

Won't this be pretty expensive?

There are currently about 17 million adresses with a balance greater than 0. One BCH is 100 million satoshis. You will need 0.17 BCH ($70.5).

Edit: unfortunately forgot about dust limit which is 546 satoshis. So you will need 92.82 BCH ($38k) for all 17 million adresses.

You could restrict the adresses to any with at least 0.1 BCH in them of which there are 1.4 million which would get the cost down to 7.644 BCH ($3130).

Will this not spam the blockchain?

A multi output transaction can fit about 300'000 outputs into a 10mb transaction (well within the capabilities of the current blocksize with room to spare). If you put one of those into each block, it will take 57 blocks to send them all (about 9 hours on average).

Drawbacks

Unless the output is used as input in a transaction, it would still be replayable on SV. Since users usually don't have control over which inputs are used, this heavily depends on wallet implementations.

It does grow the UXTO set.