You are right, El Salvador easily could gain a 6‑9% reliable yield & earn $40–60 million per year. It is very possible. But those 6-9% return is not totally risk free, is it? there are always regulatory risks caused lending section introducing smart-contract & counterparty. 
On the other hand, they are using legal loopholes to buy bitcoin, but IMF is really strict over its conditions, El Salvador must obey some rules for the $1.4 B loan deal. As part of the loan deal, they must freeze public Bitcoin holdings also halt Chivo wallet purchases. So govt are bound by the rules to move those Bitcoins to a lending platform.
Apart from this, Bitcoin Office is a separate entity, and they have its own rules. so the govt can’t officially use those BTC for lending purposes. if I make it simpler, it is actually a separate govt-owned entity, not the main treasury, so it is really foggy that using those coins for lending could run into legal or regulatory issue.
IMF rules doesn't scare Bukele. They know what they're doing and IMF has it's perceived benefits and that's why they keep borrowing El Salvador money.On the other hand, they are using legal loopholes to buy bitcoin, but IMF is really strict over its conditions, El Salvador must obey some rules for the $1.4 B loan deal. As part of the loan deal, they must freeze public Bitcoin holdings also halt Chivo wallet purchases. So govt are bound by the rules to move those Bitcoins to a lending platform.
Apart from this, Bitcoin Office is a separate entity, and they have its own rules. so the govt can’t officially use those BTC for lending purposes. if I make it simpler, it is actually a separate govt-owned entity, not the main treasury, so it is really foggy that using those coins for lending could run into legal or regulatory issue.
Bukele is committed to achieving his dream with Bitcoin and I don't see anyone stopping him, not even IMF with their noise of imposing sanctions on El Salvador for going against their agreements.
The deal does not include freezing their Bitcoin holdings or halting chivo wallet purchases, rather to stop using public funds to buy Bitcoin and making chivo wallet purchases completely voluntary.