Why do I have to use turbotax Deluxe this year to deduct Student loan interest? I've never been required to do this in previous years.

Since the tax laws changed for 2018 and beyond you would not have been able to use the Free Edition to claim student loan interest.   Student loan interest requires the use of an extra schedule that cannot be prepared using the Free Edition.   

WHY DO I HAVE TO PAY?  I WANT THE FREE EDITION

The information that you can enter in Free Edition is pretty limited now.  Thanks to the new tax laws that began for 2018 returns, there are no more simple Form 1040EZ or 1040A's.  Everything goes on a Form 1040 that has three extra "schedules" with it, and if you need any of those schedules, you are not able to use the Free Edition.  Using the standard deduction instead of itemizing does NOT mean you will not need any of those schedules.https://ttlc.intuit.com/questions/4511011-what-happened-to-the-1040a-and-1040ez   If you started in the Free Edition and entered any data that required any of those three schedules, you have to upgrade to a paid version.   The Free Edition cannot be used for self-employment income, investment income, rental income or a student loan interest deduction,

https://www.irs.gov/forms-pubs/about-form-1040 

If you qualify to use it, there is another full-featured free version of the software:

Try Free File: 

You qualify if your income was $39,000 or less, or $72,000 or less if active duty military, or if you qualify for Earned Income Credit

https://ttlc.intuit.com/questions/1900583-what-is-turbotax-free-file-program

• https://ttlc.intuit.com/questions/2026912-how-do-i-switch-to-turbotax-free-file-program

Note:  If you do not qualify to use Free File then you will have to upgrade to Deluxe or higher in the paid versions of the software.   

 Online Deluxe $40  State software $40

Or—-Use this IRS site for other ways to file for free

https://apps.irs.gov/app/freeFile/

If your TurboTax fees are higher than expected, you can reduce them by removing add-ons:

• Remove Premium Services
• Remove MAX Defend & Restore
• Remove a state
• Remove PLUS Help & Support
• Remove Pay With Your Refund