Do you mean 4 W2s or 1099s? You only get 1 refund or tax due for all your income. And you don't always get back all the withholding taken out.
You can't compare each W2 by itself to entering all the W2s. You are taxed on the Total Income and the tax rate goes up progressively with more income.
That's common. It just looks that way because you put them in as separate W2s and saw the tax due change in between them. If it all was on one W2 you would get the same answer. And each job was withholding like it was your only job.
Because you only get one standard deduction no matter how many W2s you put in. Turbo Tax starts out by giving you the Standard Deduction. You entered more income when you entered the second W2 but you didn't enter more deductions. And each job only withheld taxes like it was your only job for the year. You might want to adjust your withholding. Also as you add more income you might not be getting as many credits as before like the EIC credit. And it might have been giving you the EIC credit or some other credit until you went over.
Or did you file 4 different tax returns for different people in 4 accounts?
If by returns you mean W-2's or Form 1099's that is incorrect. The 2020 Form W-2's and Forms 1099's you received are only to be entered on only ONE 2020 tax return.
Using the online editions you can only complete and file One tax return per account and User ID.
What exactly did you do?
What do you mean by "4 returns?" Do you mean you entered four W-2's? Your income tax refund is based on the total of all of your income and the difference between your tax withheld on all of the W-2's and your tax liability. It is not "per W-2." Did you enter all of your W-2's on the same tax return? You did not try to file four separate tax Form 1040's, did you?