iPhones can indeed send SMS messages to Android. You need to check and make sure the settings are correct.
iPhone->Settings->Messages->scroll down to “Send as SMS” and make sure it is turned on. Also make sure “MMS Messaging” is turn on. If the problem is not resolved then the problem is with the Android phone, not the iPhone. The recipient may not a have a texting plan active or some such thing. And as razmee209 pointed out SMS is provided by your cellular carrier and neither Apple nor Android have control over it.
For what it’s worth I have been sending and receiving texts to and from my Android friends since day one. The vast majority of iPhone users have no problems either.