I wish more companies were so transparent and decent as yours. Why do others prefer not to do it this way, if it's not just sheer greed and obfuscation?
This approach is awesome, but (I am not a lawyer, this is not advice!) one drawback is that the whole concept of an option is that it's optional. If the company succeeds, you exercise your option and spend that money to get a much larger return. If you must buy the option, and the company does not succeed, then you've spent the money and it's gone. You've lost the "option" aspect of an option.
And of course, yes, the company may say "we're spending our money to buy this for you, don't worry" the truth is money is money. Someone (company or you) is buying the option early, thus having less money to spend on other things.
Alternatives could be the company pays you that money, so it's yours to spend as you see fit. Including, someday, buying the option if you want.
In my experience it's neither greed nor obfuscation, but rather along the spectrum of ignorance, cash conservation paranoia, and and/or a misplaced sense of justice.
Ignorance in the case of not knowing it can be done - many "startup" lawyers are operating with a playbook written in 1996.
Cash conservation in the sense of "holy schmoly I'd have to pay $X,XXX upfront in taxes to cover their option purchases???"
And "justice" in the sense of "well I'm taking a personal risk as a founder, so if you're not all in with me then suck it and your options will just go back in the pool when you quit."
In 99% of cases my guess is they just don't know it is an option because it takes extra work on the company side and is not typically something that a GC or accountant would offer.
Mostly because they don't have experience with option plans, and lawyers tend to recommend what's best for the company (not what's best for the employees).
I granted my early employee founder's stock (same as mine), mainly because I was screwed by stock options in the past. But I had to actively request this from our lawyer (the default is for lawyers to suggest stock options).
And of course, yes, the company may say "we're spending our money to buy this for you, don't worry" the truth is money is money. Someone (company or you) is buying the option early, thus having less money to spend on other things.
Alternatives could be the company pays you that money, so it's yours to spend as you see fit. Including, someday, buying the option if you want.
Hope that helps!