6 months is not 24 weeks because there are not usually 28 days in a month. There are about 52 weeks in a year (52×7=364, so a non-leap year has 52 weeks and a day), and 26 weeks would be 182 days. So 182 days is a better approximation to 6 months. 182/6=30 approximately, which is 2 more days a month than 28. That's where the difference lies: 26 weeks - 24 weeks=2 weeks, and 2×7000=14000, and 168000+14000=$182,000. That's the simple explanation.
[Another way to look at it is to use the daily rate of $1400. So, depending on where the weekends lie, there could be as little as no extra days, or as much as 3 extra days a month which come to an amount between $0 and $4,200. Take 2021, for example, the extra days are: Jan=1 extra day, Feb=0, Mar=3, Apr=2, May=1, Jun=2 (including paid holidays). Total for 2021 for first 6 months=9, amounting to 9×1400=$12,600.
Total for last 6 months of 2021=2+2+2+1+2+3=12, 12×1400=$16,800. The average of $12,600 and $16,800 is $14,700, which is close to $14,000 based on weekly earnings. Employers would probably use a simpler calculation based on weekly earnings which would provide a more balanced deal for all its employees, because of variation in individual working patterns (time on and off) and overheads such as statutory sick pay, overtime, insurance, union dues, taxes, etc. It all depends on the employment contract, so there are legal issues, too.]