It seems odd that those with 401ks are able to contribute so much more annually than those with IRAs. why are the maximum contributions for each so different?
Good question. I think it is due to tax purposes.
The IRS knows about the origin of any money going into a 401K. It has to come from legitimate income that is reported to them. IRAs are different, it involves after tax dollars. The IRS gets its cut before you put it in, but they probably don't want people bending laws by adding in illegitimate money.
401k money is not deducted on your taxes. IRA contributions are deducted.