I also would push back some against your view that interest rates must somehow rise. Nevertheless, to speculate on future moves in interest rates investors have many products at their disposal, such as outright shorting bonds, selling Eurodollar futures, or selling interest rate swaps (paying fixed), to name a few.
You are right to be hesitant about there being free money on the table. The key hurdle is that the prices for many of these products already reflect investors' expectations that rates will rise. Take interest rate swaps, for example. I have attached a screenshot from a Bloomberg Terminal's USSW screen that displays different market rates.
The 10-year swap rate is quoted at 3.241%. If you are not familiar with swaps, basically two parties are agreeing to switch fixed and floating cash flows on an agreed notional value. Let's say the notional is \$100. With today's price, you can agree to either pay fixed coupons of 3.241% (so \$3.24) a year for the next 10 years, or receive USD 3M LIBOR (currently 2.478%). The benefit of the receiving the floating side is that the floating rate you get can go up as LIBOR increases. The benefit of the receiving fixed is that the rate you receive cannot go down.
If you wanted to profit off of increasing interest rates, then you would want to pay fixed and receive floating (since you thought the floating would go up). Notice, however, that at the start you would be paying 3.241% and only receiving 2.478%, so cash would be leaving your pocket, i.e. the trade has a negative carry. Not only would you need rates to go up to make money, but they need to go up enough to overcome all this money you lose in the meantime. This negative carry reflects investors' expectations that rates will go up over the next 10 years.
Shorting bonds (particularly long-duration) would expose you to a similar negative carry position. To borrow bonds, you would need to pay a form of borrow fee (most likely through charging a lower repo rate than the GC rate, see more special in repo market). Furthermore, you would also need to pay the coupons of the bonds you have shorted to their original holders. So once again, you might have to bleed a couple percent a year to keep this trade on. Even if rates go up, you might still lose money if they don't go up enough.
The bearish rate expectations already priced into the market and the costs of implementing shorts make it so you can still lose money on your trade if rates do not go up as much as you think or do not go up fast enough.