I want to focus on this sentence:
I want to decline joining the roster since I feel like it's a lot of pressure.
Right now, the collective you of the people who do not yet participate in oncall duty have collective bargaining power. What would need to change so the pressure gets acceptable?
One of my former jobs entailed oncall duty. It was a flat amount of money, no matter how much happened. And the amount wasn't really that big.
A friend of mine currently has a job with on call duty, they get a flat amount per shift and additional money per incident.
Her regularly ups his base pay by 50%!
But pay is not the only thing:
You said in a comment it's a whole week. Where I did it, it was shifts of Mo-Fr and then Fr-Mo. So you either had the week, or the weekend. And because we could trade our shifts, I only ever did weekends, because I preferred it that way. Others only ever did during the week, because they preferred it that way! This helps a lot.
Even better if your management software and equipment allows you to split shifts more granularly. We sadly only got one oncall Laptop with the necessary permissions, we wished for two, so we could split shifts even more granularly.
E.g.: I have plans for Saturday, but could do the shift on Sunday. One laptop? This is not feasible. 2 laptops: easy going.
We had the agreement that oncall duty topics trump everything. So if something happened, we did the work to improve the situation. Documentation lacking? Write it! Monitoring configured to sensitive? Fix it! Softwarebug? Fix it!
This had prio 1 and trumped all deadlines, save for those set by the CEO.
This meant over time, we improved our infrastructure so that less incidents would happen and we could sleep more often.
This meant whole shifts passed with nothing noteworthy happening.
How is you alerting? In the beginning, everything alerted all the time. Later on, we defined ServiceLevelAgreements. This meant certain services alerted all the time, others just during 8:00-20:00. So if this was a weekend, you could at least sleep through it.
Also, what's your reaction time? If you have to react instantly, you can't do anything else. We had enough time so I could go shopping. If it happened while I was in the supermarket, I would just quite my shopping tour, pay now and rush home.
Also, pressure can come from lack of training.
You can negotiate for a level of training you will get before you get onto oncall rotation.
Also, I read studies on how bad oncall is for humans. This study didn't look at IT, but at all jobs doing oncall. And they found one killer: Frequency. Some people do oncall for a whole month, but only once a year. That's fine.
Doing an oncall day every other day is horrible, because the time off is to short to truly relax.
There are likely other points you can think about and negotiate about.
Right now, you are in a kind of Mexican stand off.
The situation is bad, and it only gets better if people volunteer. But for those who volunteer it gets worse. So everybody wants everybody else to volunteer.
If you champion for a better version of oncall duty, you can get recognition for doing so and get something out of it.
Improving the situation also prevents you being voluntold into a bad version of oncall duty. As other answers mentioned, if not enough co-workers volunteer, the business will start voluntelling.