How come many left-handed people tend to be slightly ambidextrous?

Left-handed people will be using their right hands more regularly and efficiently than the use of left hands by right-handed people. However, that does not make them ambidextrous.

Ambidexterity is the ability to use both the right and left hand equally well .

So, a left-handed can become comfortable using the objects designed for right-handed - like scissors, knives, can openers. A left-handed can be using the right hand for more activities/actions in a day.

However, he/she would be ambidextrous only if he/she could write legibly or play racket sports like tennis/badminton or throw/pitch a ball/basketball/baseball or play snooker/pool with either hand with reasonable skill.

Footnotes

Ambidexterity - Wikipedia

If you're right-handed, what are some of the things that you do with your left hand, and if you're left-handed, what are some of the things you do with your right hand?

I am left-handed, left-eyed, left-footed. I prefer left by nature and by choice if there’s an option.

Below are few things I use right hand for, by habit/adaptation/lack of choice (mostly the last one):

• While eating with hand (Indian). Will use spoon with right hand in public and left-hand at home. Sometimes, at home, I snack with left-hand if I am alone.
• Using computer mouse at work
• Turning on/off ignition key in car daily
• Steering as my left-hand is mostly on gear shift (Right-side driving in India)
• Scissors, nail cutters, knives
• Hindu religious activities when obligated - rituals like pujas, lighting lamps, putting tilak/bindi, ringing bells in temples, taking prasad/harati (arti)
• Serving food at family events (avoid as much as I can)
• Using ATM
• Dialing on my office VOIP phone
• Buttoning/unbuttoning my shirts/jackets/trousers -yeah, you can do easily with single right hand, but not with single left hand. Try yourself!
• Locking/Unlocking paddle locks
• Open refrigerator door
• Biometric reader (fingerprint scanner) at my office turnstiles entry that reads only my right index finger.
• Clicking (pressing shutter button) on my SLR camera needs my right fingers (by design), though I use my left-eye for view-finder - my nose bumps and smears the LCD screen