It’s not randomized.
Since MM is not going to find 100% perfectly balanced teams all the time, one side will generally be favored a little bit to win. The side expected to win will gain less SR for wins in that game, and side expected to lose will gain more for wins in that game.
Under 3000 SR also has performance adjustments for SR. The simplified example Scott Mercer provided assumes there is no performance adjustment (as is the case for players over 3000SR) OR you are performing exactly as you should be for your rank.
Performance adjustment isn’t randomized either, but it has not stated what is being measured to prevent people from gaming stats for SR gains.
Since you are <3000, this means you’re underperforming for someone of your SR and being nudged down.
If this is happened then you were placed too generously/boosted and grossly underperforming for your SR, and the adjustment is kicking you down to where you belong.
The only people required to maintain >50% to hold their ranks are high GM/T500s, just like how many low low low bronze players in general “need” to maintain <50% WR to stay low bronze. It takes a lot more effort to be an outlier.