Sometimes, it is just a weird accounting practice.
Here it Germany, it is common for union-negotiated salaries to include one or two extra sums, for Christmas and possibly for the summer vacation. These are not performance bonuses, they just mean an uneven distribution of the total payment across the year.
At times, the lump sum had to be repaid proportionally if the employee resigned before next spring.
For centuries, employers would give employees gifts for Christmas. In the mid 20th century, unions demanded to "regularize" the practice and to make it more predictable and fair, so those payments went into the union salary agreement.
There is some paternalism in the practice, the assumption that the poor dumb proletariat cannot be expected to manage their finances over the year and set money back for year-end celebrations and skiing vacations.
Not all employees get these non-discretionary payments. It depends on the strength of the union (stronger unions can get them) and the strength or weakness of the employee (individuals who negotiate for themselves tend to bargain either over the annual total, and not worry about 12 or 13 or 14 parts, or over the the hourly rate, and not worry about months or years).
Why is it better?
As mentioned, the extra payments are timed just before the summer and winter vacation seasons. It is really convenient to do a monthly household budget and to treat those extras as vacation funds. But not everybody can afford an expensive vacation, and not everybody goes at the same time.
And the government?
There are cases where the German government can declare a wage agreement between unions and employers' associations to be allgemeinverbindlich, generally binding. This can happen to "avoid economic mis-developments" or when an overwhelming number of employers has agreed and just a few "black sheep" remain.