It's funny how Del Shannon's music is considered Oldies, but that of The Beatles isn't. They're both from the 1960's. Actually, Del was still recording into the early-1990's, with Jeff Lynne producing.
I grew up buying 7" 45 RPM singles in the early-60's, and had quite a few before buying my first LP's (lots of instrumental Surf and "Frat" bands. And The Beach Boys). At that time Rock 'n' Roll was considered only music for teenagers, Top 40 songs heard on the radio. Those Pop songs were often written by songwriting teams, for instance those working in the little rooms in the Brill Building in Manhattan (Carole King was one such writer, while still in high school!). Then a record company music producer would pick a singer (or vocal group), arrange for studio time and a group of studio musicians (in L.A. the infamous Wrecking Crew), and endeavour to create a hit song.
There are thousands of them, all with those irresistible melodies and chorus "hooks." If I make the mistake of playing Jackie DeShannon's "When You Walk In The Room" (imo better than the cover version by The Searchers), I have to hear it another dozen times (in a row) before I'm satiated. Same with "I Fought The Law" (written by Sonny Curtis) by The Bobby Fuller Four. The song is so good even The Clash couldn't f*ck it up.
If you want to hear a killer Pop song that you probably haven't yet heard, one that you just can't get out of your head, try "Maybe" by The Chantels, a Girl Group quintet from the Bronx. Not just a great song, but the lead vocal by Arlene Smith will blow your mind. Dave Edmunds does a fantastic cover of the song on his Subtle As A Flying Mallet album.