Most of sign in reward requires deposit and wagering meaning this is not totally bonus but an obligation , though there are several site that lets us sign in and play for some spin for free yet most of those ended as scam sites or not having a fair gaming.
Bonus is not always free, even if there is deposit and wagering requirement, it is still called by bonus instead of obligation. I would prefer to see bonus for my gambling activity such as rakeback, level up bonus and other bonuses which is based on my own activity. Free bonus is good but most of the time it is not attractive due to its complicated rules behind the bonus.
and about loyalty? i cannot measure myself becoming loyal just because they gave me bonuses , instead how they treat me over the time i played.
How a casino treat us is obviously important thing and this is the main reason why gamblers stay in the casino for long time. Offering bonuses can be included in this "treat" because it is how casino try to give the best for players in all aspects.