But for understanding this verse's clear meaning we have to also know the other two verses before it. Here they are:
यामिमां पुष्पितां वाचं प्रवदन्त्यविपश्चितः । वेदवादपराः पार्थ नान्यदस्तीतिवादिनः ॥ ४३ ॥
- The undiscerning, delighting in the study of the Veda, O Pārthа, speak flowery words declaring that there is nothing else.
कामात्मानः स्वर्गपरा जन्मकर्मफलेप्सवः ।
क्रियाविशेषबहुला भोगैश्वर्यगतीः प्रति ॥ ४४॥
- They are filled with desires and have heaven as their
highest goal; during their lifetime they strive to attain the fruit of actions and prescribe many special rites for the attainment of enjoyment and power.
Now, let's check verse 45 and its relation with it.
व्यवसायात्मिका बुद्धिः समाधौ न विधीयते ॥ ४५ ॥
- A discerning state of intellect does not arise in the meditation of those who are attached to enjoyment and power, and whose minds are carried away by those flow- ery words.
So, you see here it is said so about someone who thinks vedas just as poem of flowery words, and about those who wants materialistic pleasure and want to go to heaven. Now, as Bhagavad Gita is spiritual scripture, it is more about going beyond karma. And here it is said about karma kanda imo.
Let's check commentary of Shree Abhinavgupta, great acharya of Kashmir Shaivism about these three verses above:
"Those who are overwhelmed by desire for the fruits of action perceive Vedic texts as "flowery words" (puspităm vācam). In other words, they perceive the Vedas as being permeated by the fruits of sacrifice, such as the heaven that might be attained in the future. These people accept action as the only purpose in life. This way of thinking shows that they were not properly educated. They have been misled by their wrong interpretation of the Vedas, which is the result of their own imagination. Therefore, even if they possess a decisive intellect they are not entitled to samādhi. This is because they practice samādhi in order to attain some limited result. This is in brief the purport of these three verses."
Even, Lord Shiva in Kularnava tantra mentions other shastras as 'Pashu' shastras. Why? Not to show that they are inferior to Kaula tantra shastras but because when you read any shastra, you interpret it in your way. You don't see Vedas as Vedas but interpret it yourself. That's the reason Shree Krishna also tells about this.
It is not to reject Vedas, but to make us beware to not interpret it in wrong way and also about going beyond chakra of Karma.