If you reprice equity comp each year then you lose most of the upside.
Compare the two following equity plans:
Example Year 1:
---
PLAN 1
FMV: $1
Strike: $1
Total #: 40k ISOs
Vesting: 4yrs
---
PLAN 2
FMV: $1
Strike: $1
Total #: 10k ISOs
Vesting: 1yr
---
In the second plan you get granted new equity per year targeting some total comp. This means if the equity goes up in value a lot in the first year, when your new amount is recalculated it'll be way less than 10k.
Example Year 2:
---
PLAN 1
FMV: $2
Strike: $1
Total #: 40k ISOs (10k vesting in year 2)
Vesting: 1yr into 4yr period
---
PLAN 2
FMV: $2
Strike: $2 (new grant)
Total #: 5k ISOs (The 10k from the first year, and now half that # determined by new FMV for a cumulative total of 15k instead of 20k ISOs).
Vesting: 1yr on new grant
---
This lets the company keep the majority of the upside, taking it away from employees. It also hurts employees that stay longer or have a longer term interest in the company from capturing the value they helped create.
And the more the company goes up in value, the worse the trade off becomes.
Sure in the case of a crash you may get more stock (maybe assuming they don't reduce that given hard times, target comp is just a target after all - I don't think they commit to it). Typically companies regrant underwater equity in the case of a crash anyway (see peloton). Even in the best case, I'd guess it's unlikely the grants during a down year make up for being excluded from being able to get more at a lower price 5yrs out.